Runa Tsukimi

Runa Tsukimi is one of Yonosuke Sakai’s childhood friends and functions as a key heroine in the story.

She is a year younger than Yonosuke and fills the classic “little sister” role in his life, both in age and in how she relates to him.

She is commonly nicknamed “Runako.”

Runa has light purple twin-tail hair and a bright, playful demeanor that stands out among the cast.

Runa calls Yonosuke “big brother,” emphasizing her position as a younger, sister-like childhood friend.

Despite this, she does not hide that her feelings for him are romantic rather than purely familial.

Runa is cheerful, innocent, and energetic, often acting with the straightforward boldness of someone who has not fully outgrown her childhood.

Her behavior is easygoing and affectionate, but there is a hint of calculated charm beneath the surface.

She leans heavily into her “little sister” character, using it as a way to get close to Yonosuke.

At the same time, she can be surprisingly crafty and knowingly cute, showing a deliberately “sly” side when pursuing him.

The gap between her innocent appearance and her sometimes mischievous romantic advances is part of her appeal.

She is frequently framed as an angelic yet slightly devilish little-sister type, walking the line between pure and teasing.

Runa is depicted as a young girl with light purple hair styled in twin tails, which reinforces her youthful and energetic image.

Her overall look highlights her role as the younger, little-sister heroine.

Although she is still in middle school, her figure is noted as being fairly well-developed for her age.

She is not as voluptuous as Shio Minamo, but she is still described as having a comparatively larger chest for a middle school student.

Her design emphasizes cuteness and approachability rather than maturity.

The combination of her hair color, hairstyle, and expressive demeanor makes her visually distinctive within the cast.

Runa is introduced as one of the main heroines surrounding Yonosuke in "You Can't Be In a Rom-Com with Your Childhood Friends!"

She is positioned as both a nostalgic presence from his past and a fresh source of romantic tension in the present.

Five years before the events of the main story, Runa moved away from Yonosuke’s hometown.

Despite the distance, the bond from their childhood remained important to her.

She later returns alone to Yonosuke’s hometown in order to attend high school there.

Until spring, she stays as a live-in guest at Yonosuke’s house, turning their relationship into an unexpected cohabitation situation.

During this shared living arrangement, Runa openly and consistently makes romantic advances toward Yonosuke.

Among all the heroines, she is described as the one who appeals to him the most directly and straightforwardly in love.

Her presence complicates Yonosuke’s daily life, balancing domestic familiarity with heightened romantic awareness.

The tension between “she’s like a little sister” and “she is clearly in love with him” becomes one of the central dynamics of her character.

Yonosuke Sakai

Yonosuke Sakai (nicknamed “AU”) is the protagonist and Runa’s older childhood friend.

For Runa, he is both a nostalgic “big brother” figure and the person she is actively in love with.

She addresses him as “big brother,” reinforcing their long-standing closeness and her carefully maintained younger-sister persona.

At the same time, she uses that intimacy as a springboard for bolder romantic actions.

Yonosuke, being older by one academic year, tends to see her as someone to look after.

Runa frequently challenges this perception by making it clear that she wants to be seen as a girl and as a romantic interest, not just as a kid sister.

Other Heroines

Runa’s figure is contrasted directly with that of Shio Minamo, who is described as more well-endowed than Runa.

This comparison highlights Runa’s own physical development while also setting up a playful rivalry in terms of feminine appeal.

Among the heroines orbiting Yonosuke, Runa stands out as the most open and persistent in her love appeals.

Where others may be hesitant or indirect, Runa is unabashedly forward, making her feelings easy to read.

Runa Tsukimi is voiced by Sai Hiratsuka.

The voice performance emphasizes her bright, innocent tone while also capturing her sly, teasing nuances as a “little sister with a devilish side.”