Shiina Usami

Name: Shiina Usami

Gender: Female

Age: 16 → 17 (16 at Rentarou’s entrance ceremony, later turns 17)

School: Ohana no Mitsu University Affiliated High School, Year 2, Class 6

Birthday: April 17

Zodiac Sign: Aries

First appearance (manga chapter): Chapter 169 (first clearly introduced and linked with Rentarou; her eerie “blend‑in” appearance is in Chapter 168)

“Bibiiin!!” fated encounter chapter: Volume 20, Chapter 169

Girlfriend join chapter: Volume 20, Chapter 169

Self‑nickname: “Usa‑chan” (“Bunny‑chan”)

First‑person pronoun: “Watashi” (standard “I”) in the original Japanese

Visual concept: Landmine‑style gal, black as base color with pink accents

Implied image color: A soft, slightly purplish pale pink similar to “rose dragée” (inferred from official birthday illustration background)

Shiina Usami is Rentarou Aijou’s 28th fated girlfriend and becomes a member of the ever‑expanding Rentarou family polycule.

She is classified in the design notes as a landmine‑style gal, following Karane Inda and Aashii Kedarui as the third main “gal” heroine of the series, though with a distinct fashion flavor.

Her visual theme is black plus pink, with fluffy, soft pieces to emphasize comfort and “healing.”

She is strongly associated with rabbits, both in hairstyle and accessories, and is often visually simplified into a cute black bunny form in gag panels.

Shiina is notably tall, standing slightly taller than Rentarou and ranking as the second tallest member of the family, just above Mimimi Utsukushisugi and only shorter than Yamame Yasashiki.

Her overall silhouette leans long and slender, which makes her clingy body language stand out even more.

Her signature hairstyle resembles rabbit ears:

Her braids are folded up and secured with fluffy scrunchies, creating a bunny‑ear look.

She has long side strands framing her face like “antenna” bangs, reinforcing the cute, slightly unstable “landmine” feel.

Her base hair color is black, with pink mesh highlights added in her normal appearance.

When she is shown as a child or in “babyfied” versions, the pink highlights disappear, matching her natural hair color.

Her clothes are mostly:

Black tops and skirts or dresses, often with lace or frills.

Pink accents on accessories, trims, or prints.

Cardigans and other fluffy items that feel warm and comforting to touch.

Her rabbit motif goes beyond hair:

A rabbit‑shaped plushie lives in her pocket; its expression sometimes changes in sync with Shiina’s emotions.

Her left ear earring is shaped like a rabbit.

Her front teeth and braids further evoke a rabbit image and are often emphasized in close‑up panels.

In comedic scenes, just as Tama Nekonari is sometimes drawn as a simplified black cat, Shiina is often drawn as a chibi black rabbit, visually underlining her nickname “Usa‑chan.”

Extreme Fear of Loneliness

Shiina defines herself as “extremely lonely” to the point of feeling like she might literally die when she is alone.

She jokingly describes this as “reverse trypophobia of crowds” turned inside‑out: she hates emptiness and isolation instead of clusters and density.

She:

Fears “sparse” or “empty” spaces, such as being the only person in a wide area.

Loves crowded, packed environments – “crammed” and “jam‑packed” situations make her feel safe.

Even purposely rides packed commuter trains just to be surrounded by people and calm her anxiety.

When her fear spikes, she uses phrases like “I’ll die of loneliness”, turning loneliness into a quasi‑literal death flag gag.

She even dislikes seeing shelves with empty spots and wants everything tightly filled and aligned.

At school, her loneliness manifests in everyday habits:

She hates eating lunch alone and tries very hard to avoid it.

She avoids going to the restroom alone, sometimes holding it in rather than face walking there by herself.

This is presented as comedic exaggeration but underscores how serious her discomfort with solitude is.

Clinginess and Distance Problems

Because she “cannot stand being alone,” Shiina ideally wants to always be with someone.

However, her attempts to stay close often become too intense, which has historically caused people to pull away from her.

Her typical behaviors with someone she cares about include:

Repeating their name constantly in conversation.

Getting physically very close, hugging, leaning, or hanging onto them.

Sending huge numbers of messages via chat apps when they are apart, far beyond normal frequency.

These behaviors have made her anxious about friendship itself.

She is afraid that her clinginess will make people think of her as annoying or suffocating, which leads to a painful loop: wanting closeness, going all‑in, then withdrawing in self‑loathing once she senses discomfort.

At the same time, she is not selfish or malicious.

When she notices that someone is bothered, she:

Pulls back on her own initiative.

Falls into self‑deprecating guilt.

Accepts criticism and tries to correct herself, showing that she has solid morals and empathy.

Coping Mechanisms

When real‑world connection fails or is not available, Shiina looks for substitutes to soften the loneliness:

She plays online games such as competitive platform fighters, using anonymous online matches to feel the presence of “someone, somewhere” interacting with her.

She talks to a voice‑mimicking plush toy that repeats her words back to her in a robotic echo, effectively turning her own voice into “another person” to converse with.

Example:

Shiina: “Hello!”

Plush: “Hello!”

Shiina: “What are you doing today?”

Plush: “What are you doing today?”

These scenes highlight how desperate she is to avoid being the only voice in a room.

Nickname and How Others Address Her

At her introduction, Shiina explicitly asks others:

> “Everyone, it would make me happy if you called me ‘Usa‑chan’ with affection!”

As a result, within the Rentarou family she is almost always called:

“Usa‑chan” (sometimes plus an honorific like “Usa‑chan‑senpai”)

Or simply “Usa”

Her given name “Shiina” is used very rarely in dialogue.

Unlike Nadeshiko Yamato or Aashii Kedarui, whose nicknames derive from their given names, Shiina’s nickname is based on her surname “Usami”, making her the first girlfriend who is, in practice, not addressed by her given name (except by a few rare characters like Nano Eiai, who tends to use full names).

Constantly hearing “Usa‑chan” from many people acts as a verbal security blanket for her, reinforcing that she is “included” and not alone.

The “Who Is This Girl?” Introduction

Shiina’s first appearance is one of the most unsettling and memorable gags in the series.

In Chapter 168, during a usual rooftop Rentarou‑photo trading session among the girlfriends, she is simply there, naturally mingling and swapping bromide photos as if she has always been part of the group.

She:

Chatters casually with the other girlfriends.

Demonstrates detailed knowledge of each member’s personality, preferences, and relationship with Rentarou.

Fits in so smoothly that no one initially calls out the weirdness.

It is only when Rentarou himself, deeply confused, finally interrupts with something equivalent to:

> “Who? Who are you?”

that the girls collectively realize they do not know who she is either, even though they have all been interacting with her.

The combination of:

No name reveal.

Her eyes never fully opening in front of Rentarou.

The fact that Chapter 168, based on series patterns, should have been a new “Bibiiin!!” fated encounter chapter.

left readers very unsettled and eager for answers.

It was the first time the series introduced an important new girl in such a stealthy, almost horror‑adjacent way.

This confusion was compounded by:

The previous week being a serialization break, making some readers wonder if they had missed a chapter.

The volume edition placing this strange chapter at the very start of Volume 20, which made some volume readers fear they had skipped a whole book.

The magazine’s promotional text even leaned into the weirdness with an ominous tagline roughly equivalent to:

> “If she isn’t a Bibiiin!! girl, this is way too scary!!”

Background of Her Obsession With the Rentarou Family

The full explanation comes in Chapter 169, telling Shiina’s side of the story.

One day, she noticed the Rentarou family — an enormous group of girlfriends walking around together, always packed, cuddling, and radiating overwhelming happiness.

Given her extreme fear of loneliness, this group represented:

Her ideal density of human connection.

A moving, living proof that a huge, unconventional relationship could still be full of genuine joy.

She secretly observed them over time, picking up:

Each member’s name.

Their typical behavior and quirks.

How they related to Rentarou and to each other.

At first, she was naturally shocked to learn that:

All of these girls were Rentarou’s girlfriends.

The relationship was openly polyamorous, with everyone participating and genuinely happy.

However, as she watched longer, her impression changed:

> Everyone truly looked happy from the bottom of their hearts.

> Compared to a standard one‑on‑one romance, she felt there was “even more happiness” concentrated in this arrangement.

In her own words, the Rentarou family became:

> “The most wonderful form of love in the world, at least for me.”

This deep admiration — combined with her longing never to be alone again — led her to attempt something bold:

She slipped into the group and pretended she had always belonged, hoping to become part of that dense, comforting “population mass.”

Confession, Misunderstanding, and Runaway

Eventually, Shiina cannot just lurk and blend forever; she gathers her courage to directly ask Rentarou:

She confesses she wants to join the Rentarou family.

She asks Rentarou to go out with her.

However, Rentarou does not answer immediately.

He hesitates for a moment, intending to phrase his response thoughtfully.

For Shiina, who is extremely sensitive to rejection and loneliness, that small pause feels like a catastrophic refusal.

She believes she has just been dumped and, overcome by the feeling of being abandoned and alone again, bolts from the scene like a startled rabbit.

She runs through the city in emotional panic and ends up boarding a packed train as an emergency coping measure.

At first, the body‑to‑body crush of the crowded carriage soothes her loneliness, but the emotional overload eventually becomes too much: the density becomes suffocating instead of comforting.

Just when it seems like she might “die of loneliness in a crowd,” Rentarou finally catches up to her.

He manages to pull her off the train, and the two wind up in an almost empty station, a jarring contrast that immediately makes Shiina feel emotionally “sparse” again.

Rentarou’s Answer and Official Family Entry

At the deserted station, Rentarou finally explains what he really wanted to say.

He tells her that:

She called his family — the thing he loves more than anything — “the most wonderful form of love in the world”, which made him very happy.

He wants to date her, not just because she wants to join the family, but because he truly wishes for her to be included and cherished.

He also insists on a principle:

If her only reason is “I want to join the family,” he does not think that alone is enough for her to feel she has the right to date him.

So he asks her to allow him the chance to make her fall in love with him more deeply, promising to put in the effort.

However, the frantic chase and his heartfelt actions have already done their work.

By the time she hears this, Shiina realizes she has long since fallen for Rentarou himself, not just the idea of the group.

With this mutual understanding, she:

Accepts his feelings.

Officially becomes Rentaro’s girlfriend and a full member of the Rentarou family.

The serialization teasingly labels this moment with a phrase akin to:

> “Packed even tighter, updated!”

artfully tying her love of density and crowds back into her joining the increasingly crowded family.

Shiina’s daily routine is heavily shaped by her need for constant emotional presence.

She tends to:

Hug or cling to people she likes without much restraint.

Verbally affirm affection repeatedly, using name‑calling as a form of self‑soothing.

Seek out places where many people naturally gather, like trains or busy corridors.

She can handle team sports, where she is surrounded by others, but individual sports are psychologically unbearable.

For example, the idea of skating alone on a big ice rink feels to her like exile to Antarctica, more like torture than exercise.

When she is in a balanced environment, such as the Rentarou family where many people can share the “load” of her needs, she becomes:

Bright.

Playful.

Intensely affectionate, but in a way that can be safely distributed among many partners.

The series jokingly suggests that, without the Rentarou family, she might have eventually “died of loneliness one way or another”, both in the sense of emotional collapse and in the absurd gag sense that the story loves to employ.

Rentarou Aijou

Rentarou is Shiina’s fated soulmate and the core of the polycule she adores.

He responds to her clinginess not with annoyance but with genuine appreciation and love.

Very early in their relationship, Rentarou tells her something to the effect of:

If she ever feels like she has to hold back her affection or loneliness around him, that is a failure on his part as her boyfriend.

He exaggerates that he will “punch his own face until it doubles in size” as punishment if he makes her feel that way.

This declaration gives Shiina permission to be emotionally honest and unreserved.

She proceeds to:

Send him over a thousand messages a day, continuing lively back‑and‑forth conversations.

Call his name endlessly: “Rentarou‑kun, Rentarou‑kun, Rentarou‑kun…”

Even, at one point, uses a ladder to climb into his room because she wants to be needed and physically close.

Far from being freaked out, Rentarou is delighted, openly thinking that being loved so aggressively by “Usa‑chan” makes him feel incredibly happy and privileged.

Their relationship becomes a kind of mutual feedback loop of affection, where her clinginess is finally met by someone who can return and handle it.

Mimimi Utsukushisugi

Mimimi is a same‑grade girlfriend, though in a different class from Shiina.

Mimimi calls her “Usa‑chan‑san,” adding a slightly formal twist that underscores both affection and respect.

At one point, Mimimi notices how anxious Shiina is about “smothering” people with her need for closeness.

Shiina explains that whenever she gets close to someone, she:

Ends up sticking to them constantly.

Repeats their name obsessively.

Keeps messaging them non‑stop even when apart.

Eventually, this leads to the other person distancing themselves.

Mimimi, whose own theme revolves strongly around notions of inner beauty and consideration, comes up with a plan:

She tells Shiina that if she needs somewhere to pour her affection and loneliness, she should direct it toward Mimimi.

Shiina immediately takes this advice extremely literally:

She unleashes a rapid‑fire barrage of “Mimimi‑chan, Mimimi‑chan, listen, listen!”

She calls her name dozens of times in a row.

She even follows Mimimi all the way to the restroom, accompanying her right up to the stall door, chattering “Mimimi‑chan♥” in patterns so dense that the manga typesets them in blocky, wall‑like shapes.

Mimimi tries to respond in kind, repeating “Usa‑chan‑san” again and again, pushing herself to keep up.

But Shiina, perceptive despite her anxiety, can see that Mimimi is forcing herself and is starting to strain.

Realizing she has once again gone too far, Shiina prepares to pull back, ready to sacrifice her own happiness to avoid burdening Mimimi.

This moment of self‑restraint impacts Mimimi deeply.

Mimimi thinks:

Rentarou would never let Shiina make such a pained, lonely face.

Her own heart, while kind, still feels inferior to Rentarou’s, but she doesn’t want to be the cause of Shiina’s sadness.

She then reaches out to the Rentarou family, asking them to help share the weight of Shiina’s affection and needs.

With the entire family willingly requesting Shiina’s attention and hugs, Shiina is finally able to feel “needed” by many people at once without overloading any single individual.

Shiina then thanks Mimimi, telling her:

> “I think your heart is already as beautiful as Rentarou‑kun’s.”

This line completely wins Mimimi over emotionally and further solidifies their warm, mutually admiring relationship.

Mimimi does, however, gently correct Shiina that following someone into the actual bathroom stall is crossing a line, helping her calibrate her sense of appropriate distance.

Other Friends and Characters

Nano Eiai

Nano is notable for her habit of using full names, and she is one of the very few who refers to Shiina as “Shiina Usami” instead of “Usa‑chan.”

This makes Nano an unusual case in Shiina’s social circle, as she thereby highlights Shiina’s actual given name more than most.

Kishika Torotoro

Kishika jokingly comments on Shiina’s tendency to claim she might “die of loneliness,” retorting in her blunt knightly way that Shiina is far more likely to die from some completely different cause first.

This becomes a little running gag that undercuts Shiina’s melodramatic phrasing.

Tomodachi Dynamics: Komari and Others

Shiina is labeled as having trouble with “friend distance” and becomes close with characters who share similar issues managing interpersonal boundaries.

For instance, she goes on outings like shopping trips with other socially awkward girls and seals friendships with exaggerated promises such as being “friends forever and ever for all eternity,” leaning right into her fear of being left behind.

In these friendships, Shiina often takes the initiative, inviting others out and modeling a kind of vulnerable honesty about her needs, which can be surprisingly helpful to characters who are used to isolation.

Parents

Shiina’s parents appear in a bonus chapter in Volume 20.

They affectionately call their daughter “Shiina‑chan”, which is notable because:

Almost everyone else in the cast calls her “Usa‑chan.”

Hearing her given name used warmly emphasizes that her extreme loneliness issues are not due to parental abuse or neglect.

They share her family name “Usami,” of course, but otherwise do not display the same intense fear of loneliness.

Shiina’s condition is portrayed as something tied more to her innate temperament than to her upbringing.

The Ramen Shop Owner

A female ramen shop owner first appears in Chapter 83 as the creator of a large “challenge ramen” that the Rentarou family once conquered.

In Chapter 220, this owner returns after undergoing “training” and unveils a new dish: “Ultra Cluster Ramen” — a bowl filled with a nightmare‑inducing number of tiny deep‑fried crabs, meant to trigger trypophobia‑like discomfort in those who fear clusters.

She expects this to be a horror dish, but to Shiina it is the opposite:

The sheer amount of tiny pieces tightly packed together is comforting.

Shiina cheerfully eats through the entire thing, joyfully commenting that it feels “jam‑packed in her stomach” and that everything inside her will always be together.

The owner is once again completely defeated by the incomprehensible tastes and capacities of the Rentarou family, especially Shiina’s inversion of normal revulsion into delighted acceptance.

Shiina Usami’s name likely carries several layered wordplays:

“Usami” sounds like “usa” (bunny), syncing with her rabbit motif.

“Shiina” can be broken as “shi” (4) and “ina” (17), making a 4/17 date, matching her birthday.

Combining the sounds can hint at “samishii na” (“so lonely”), echoing her loneliness theme.

Her family entry number, 28, also seems intentionally playful.

If you flip “28” to “82,” you get a sound pun resembling “bunny” in Japanese wordplay, further tying her to rabbits.

Within the story, she is:

Almost always referred to as “Usa‑chan” or “Usa,” not “Shiina.”

The first girlfriend whose widely used nickname is drawn from her surname rather than her given name, making her actual first name comparatively rare in dialogue.

In 2025, on March 3rd, the official 100 Girlfriends social‑media account accidentally celebrated both Mimimi Utsukushisugi’s and Shiina’s birthdays on the same day.

In reality:

Mimimi’s birthday is correctly on March 3rd.

Shiina’s is on April 17th and was only clearly revealed under the cover flap of Volume 20.

Because March 3rd is sometimes informally called “Rabbit Day” in Japan due to number puns, some fans found the mistaken birthday plausible and did not immediately realize it was an error.

The post was later deleted, but many fans responded warmly, joking that it was very “Usa‑chan‑like” to want to be celebrated together with Mimimi.

Finally, Shiina’s true birthday of April 17th happens to match the birthday of Nozawa, the series’ artist, further suggesting that her date and name gags were carefully chosen and not accidental.