Eru Aharen

Eru Aharen is the younger sister of Reina Aharen and a main heroine-level character in her own right.

She is three years younger than Reina and currently attends middle school.

Within the Aharen family, she is the older sister of Ren Aharen and the daughter of Ai Aharen and En Aharen.

She appears after Reina and Shōta Raidō advance to their second year of high school in the original manga, but her appearance is moved up significantly in the anime, where she first shows up in episode 8 during their first year.

Eru is voiced by Rina Hidaka in the anime adaptation.

She becomes involved in the story through her concern for Reina and her complicated feelings toward Raidō, whom she believes is the most important person in Reina’s life.

Eru strongly resembles her sister Reina, especially in facial features and overall vibe.

However, several distinct traits set her apart and make her visually striking.

Her eyes are notably sharp and piercing, often compared to those of a snake, which gives her a more intimidating look than Reina.

She is tall for her age, with a noticeably greater height than her sister.

She has long silver hair that she wears in a straight, flowing style.

In contrast to Reina’s petite build, Eru has a more mature figure, with a prominently well-developed chest, which the narrative occasionally highlights for comedic effect.

Eru is a classic tsundere: she acts harsh and cold on the surface but is actually very kind and caring underneath.

She loves Reina deeply and worries about her more than anyone else.

Because she is convinced that Raidō is the most important person to Reina, Eru tends to treat him bluntly and even harshly.

Despite this, she does not actually disapprove of Reina and Raidō’s closeness; she is simply too awkward and embarrassed to be honest about her feelings.

Eru is at a difficult, sensitive age and struggles to express herself straightforwardly.

She deliberately hides her day-to-day acts of kindness from Reina, trying not to let her sister notice how much she looks out for her—though Reina, of course, notices anyway.

When praised or flustered, Eru easily blushes, betraying her softer side.

Overall, she is deeply sister-loving, a bit prideful, easily embarrassed, and very gentle at heart.

Eru has a distinctive verbal tic that functions as her catchphrase.

She frequently ends her sentences with a phrase equivalent to “you know” or “and all,” which gives her way of speaking a slightly quirky, memorable rhythm.

Her sharp gaze and tall stature can make her seem unapproachable at first.

However, her reactions—such as blushing and getting flustered—often undercut that impression and reveal how sensitive she actually is.

Eru is notably bad at using UFO catchers (crane games), despite her earnest efforts.

Even so, she tries to win prize items with her own allowance as gifts, especially for Reina, showing how she expresses love through actions rather than words.

Reina Aharen

Reina is Eru’s beloved older sister and the person she cherishes most.

Eru constantly worries about Reina’s well-being and tries to support her behind the scenes.

She cooks for Reina when Reina catches a cold and has to stay home from school.

She also attempts to get prize items by herself to make Reina happy, even though she is terrible at crane games.

Although she tries to keep these gestures hidden and act indifferent, her entire behavior is rooted in wanting Reina to be safe, healthy, and happy.

Their bond is very strong, built on quiet acts of care and unspoken understanding.

Shōta Raidō

Raidō is Reina’s close classmate and the male lead of the series.

Eru sees him as the person most important to Reina and, because of that, often treats him rather harshly.

Her attitude toward Raidō is not rooted in dislike but in awkward jealousy and protectiveness.

She is embarrassed by how much she cares about Reina’s happiness, so she masks it by being strict or prickly toward Raidō.

Despite the sharp tone she often takes with him, she does not deny or reject the idea of Reina and Raidō being close.

On some level, she seems to accept their relationship but has trouble openly acknowledging her approval.

Ren Aharen

Ren is Eru’s younger brother, making her both a younger sister to Reina and an older sister to Ren.

Although the text does not go into detail about their direct interactions, Eru sits in the middle of the sibling order, giving her both protective and admiring roles within the family.

Ai Aharen and En Aharen

Ai Aharen is Eru’s mother, and En Aharen is her father.

Eru inherits aspects of the Aharen family’s distinctive appearance, especially the resemblance to Reina.

The family dynamics are largely depicted through comedy in the series, and Eru’s tsundere tendencies fit neatly into the slightly eccentric Aharen household.

Raidō’s Little Sister

Raidō’s little sister attends the same middle school as Eru.

After they realize that their older siblings—Reina and Raidō—are close to each other, the two younger siblings begin to interact more.

This leads to a friendly relationship between Eru and Raidō’s little sister.

Their shared perspective as younger siblings of an unusual duo helps them bond and maintain a positive, easygoing connection.

Eru first appears in the original manga in chapter 83, after Reina and Raidō move up to their second year of high school.

Her introduction expands the world of the series by bringing in more of Reina’s family and showing how Reina’s relationships affect those around her.

In the anime adaptation, Eru’s debut is moved up to episode 8, when Reina and Raidō are still first-year students.

This earlier appearance allows the anime to include more of Eru’s dynamic with Reina and Raidō and to showcase her tsundere charm sooner.

Eru mainly functions as a secondary heroine who:

Highlights Reina’s importance to others through her intense protectiveness.

Adds comedic tension through her harsh-but-actually-caring treatment of Raidō.

Provides a middle school perspective and expands the cast’s age range and school settings.

Eru introduces herself formally as “Reina Aharen’s little sister, Eru Aharen,” emphasizing her identity in relation to Reina.

Her self-introduction fits her somewhat stiff, easily embarrassed personality.

The school swimsuit that Reina uses for swimming class in middle school is actually a hand-me-down from Eru.

It is the swimsuit Eru wore in elementary school, with “6-3 Aharen” written on the chest to mark her former class and name.

When Eru graduated to middle school and no longer needed that swimsuit, she passed it on to Reina.

This detail quietly underlines their close-knit sibling relationship and the everyday way they share and reuse things within the family.

Eru’s poor performance with UFO catchers is a recurring gag.

Despite her lack of skill, she stubbornly keeps trying to win prizes with her own allowance, especially for Reina, which makes her efforts both funny and touching.