Chiaki Hoshinomori is a reserved and introverted girl who often keeps to herself. Initially indifferent to her appearance, she preferred spending time alone, immersed in video games, rather than socializing with others. Her solitary lifestyle began to change after she met Keita Amano and Tasuku Uehara, who gradually influenced her to open up.

Online, Chiaki operates under two separate aliases: “MONO” as a player and “Nobe” as a game developer. These identities allow her to engage in the gaming community while maintaining anonymity in real life.

Chiaki initially bonded with Keita over their shared preference for gaming as a hobby rather than a competition. Both rejected Karen Tendō’s invitation to the Game Club for similar reasons. However, despite this common ground, the two often clashed due to differing opinions on games, leading to frequent and sometimes petty arguments. Still, Chiaki demonstrated a degree of trust in Keita, as seen when she instinctively ran to him for help after being approached by flirtatious boys at the pool.

Her perception of Keita changed drastically after she discovered that he was unknowingly both of her cherished online companions “Tsucchi” and “Yama” with whom she had formed deep bonds. The revelation left her in emotional turmoil, and she struggled to reconcile her real-life tensions with Keita and her online admiration for him. Once she regained her composure, she became noticeably more flustered and awkward around him, developing strong romantic feelings but feeling conflicted due to his existing relationship with Karen.

Unable to confess, Chiaki chose to conceal her online identities by falsely claiming they belonged to her younger sister. Despite her insecurities and the rocky history between them, she was deeply moved when Keita expressed that he still valued their connection. Overwhelmed by the moment, she nearly confessed her feelings but stopped herself upon realizing she was acting impulsively. Encouraged by her sister and driven by her own emotions, Chiaki became determined to gain Keita’s attention displaying a newfound resolve that surprised even those closest to her.

Chiaki Hoshinomori is a teenage girl of average height with violet-tinted eyes. She is considered attractive by several characters, including Tasuku Uehara. Initially, she had long, dark blue hair that nearly obscured her eyes. After Keita Amano jokingly referred to her as a “Seaweed Girl” because of her bangs, and Tasuku suggested she would look better with shorter hair, Chiaki decided to cut her hair and has worn it short ever since.

At school, she wears the standard Otobuki High School girls’ uniform, similar to Karen Tendō’s. Outside of school, she is occasionally seen in casual attire, which varies depending on the setting.

Chiaki Hoshinomori is a devoted gamer who enjoys playing video games for fun, regardless of her skill level. In addition to playing, she is also a game developer known for creating titles that often diverge from mainstream trends. Her love for gaming extends beyond casual interest and has become a defining part of her personality.

At one point prior to the main events of the series, Chiaki was invited by Karen Tendō to join the Game Club. However, she declined without hesitation, explaining that while the members were undoubtedly skilled, their competitive approach to gaming did not align with her personal style.

Chiaki first meets Keita Amano in class while both are playing games on their devices. Initially shy and awkward around him due to their unfamiliarity, she quickly asserts that she has no interest in joining the Game Club. However, she is surprised when Keita reveals he had also rejected the same invitation for similar reasons. Bonding over their shared philosophy on gaming, the two quickly grow close, exchanging messages and supporting each other in various games. Their budding friendship attracts the attention of Karen Tendō, who begins to suspect that they might be romantically involved.

Tensions arise between Chiaki and Keita when they begin to argue over their differing opinions on games. Their bickering irritates Tasuku Uehara, who intervenes to ease the tension and teasingly suggests that Chiaki would look cute with shorter hair—after Keita jokingly calls her “Seaweed Girl” due to her long bangs. Following this, Chiaki decides to cut her hair, marking a turning point in her character development.

Their interactions unintentionally spark a chain reaction of misunderstandings: Aguri Sakurano begins to suspect Tasuku of cheating, Keita and Aguri grow closer as friends, and Karen becomes increasingly jealous of Keita and Chiaki’s relationship. Despite their strained rapport, Chiaki quietly supports Keita’s decision to ask Karen out on a date.

During Keita and Karen’s date, Chiaki runs into them at the pool and asks Keita for help when she’s harassed by other boys. Although the moment is awkward especially given Karen’s veiled jealousy Chiaki explains she was searching for her younger sister and ends up joining the couple, unintentionally becoming a third wheel.

Later, Chiaki invites Tasuku, Keita, Aguri, and Karen to her home for a board game night in an effort to clear the air between everyone. During the gathering, she steps out briefly to talk with her sister, Konoha Hoshinomori, and inadvertently overhears a conversation revealing that Keita is her cherished online gaming companion both “Tsucchi” and “Yama” leaving her stunned and emotionally shaken.

After regaining composure, Chiaki seeks advice from Konoha, but their conversation offers little clarity. She unexpectedly runs into Keita while shopping, and upon learning he lost his transit pass at her house, invites him over to help find it. Though she secretly locates the pass, she stalls his departure in an attempt to spend more time with him. When Keita nearly discovers her online identities, Chiaki hastily lies, claiming they belong to her sister. Konoha, waking up during the encounter, plays along and pretends to be both “MONO” and “Nobe” to protect Chiaki’s secret.

In Volume 5 of the light novel, Konoha consults Keita to help find a birthday gift for Chiaki, based on their shared interests. Unaware of his involvement, Chiaki is touched by the present and expresses heartfelt appreciation.

Despite still being conflicted, Chiaki continues to spend time with the group. She joins Keita, Karen, Tasuku, and Aguri on a double date at an amusement park, accompanied by her sister. During the anime-exclusive Kizuna Dungeon scene, Chiaki collapses from dizziness and is carried to a bench by Keita. Upon waking and learning what happened from Konoha, she is stunned when Keita expresses how much he values their connection, despite their troubled past. Momentarily overwhelmed, she nearly confesses her feelings but stops herself, choosing instead to remain by his side and enjoy the day.

Chiaki later tells her sister that while she cannot confess her love to Keita yet, she is determined to win his attention one day displaying a sense of motivation and emotional growth that surprises even Konoha.

The given name Chiaki (千秋) is composed of the kanji chi (千), meaning “thousand,” and aki (秋), meaning “autumn.” Her surname, Hoshinomori (星ノ守), combines hoshi (星), meaning “star,” and mori (守), meaning “guardian.”