Kyō Nukui is the main protagonist of the series. He is a fifteen-year-old first-year student in the general studies course at Niida West High School. Despite being enrolled, he has not attended a single class since entering high school. This is a continuation of a pattern that began in his middle school years, when he became a shut-in and stopped attending school altogether. The root cause of his withdrawal is a traumatic event from his childhood: during elementary school, he wrote a poem for a class assignment that was praised by his teacher but ridiculed by his classmates, who gave him a derogatory nickname and continued to mock him through middle school by circulating copies of his writing. This experience caused him to develop severe social anxiety and a deep fear of exposing his inner self to others.

During his time as a shut-in, Kyō discovered a passion for music. He taught himself to play the guitar and began composing songs using vocal synthesizer software. Under the online pseudonym HibikiP, he uploaded his original music to video-sharing websites, where his work gained a modest following. He also collaborated with an online artist who went by the name Kiriyume, who provided illustrations for his songs. Music became his sole outlet for self-expression and his only connection to the outside world.

Kyō's personality is defined by a combination of gentleness, seriousness, and deep-seated insecurity. He is fundamentally a kind and thoughtful person who cares about the feelings of others, but his trauma has made him extremely self-conscious and hesitant to take initiative in social situations. He tends to keep to himself and avoids drawing attention. However, he also possesses a quiet determination, and when he finds something worth pursuing, he can push past his own fears. This is evident in his decision to return to school after being asked to help the girls, a direct consequence of his desire to support them and a recognition that he needs to confront his own issues.

His primary motivation at the start of the story is simply to cope with his daily life through music. This changes dramatically when he is contacted by a fan who turns out to be three elementary school girls: Jun Goto, Nozomi Momijidani, and Sora Kaneshiro. They live at an orphanage called Little Wing and have formed a rock band using vintage instruments owned by the orphanage's guardian, Masayoshi Sawatari. They ask Kyō to help them with an upcoming concert. Initially hesitant, Kyō is deeply impressed by their musical skill and genuine passion. Despite Mr. Sawatari's request that he discourage them, Kyō ultimately agrees to help. His motivation shifts from passive escapism to active engagement: he wants to help the girls achieve their goal, and in doing so, he begins to take steps toward his own recovery.

Kyō's role in the story is that of a catalyst and a mentor. He provides the girls with musical guidance, acts as their producer and composer, and helps them organize their performances. He is the person who connects their raw talent to the real world. At the same time, the girls serve as his catalyst. Their trust in him and their dependence on his help force him to leave his room and re-engage with society. The story is as much about his personal growth as it is about the band's journey.

Kyō's key relationships are central to his development. His younger sister, Kurumi Nukui, is an elementary school student who is far more mature and responsible than he is. She manages the household in their parents' absence, is a class representative, and is deeply worried about her brother. She often scolds him but also supports him unconditionally. Sakura Toriumi is a classmate and childhood friend who transferred to his school in middle school. She is an orphan from Little Wing and acts as an older sister figure to the three girls. She secretly has feelings for Kyō and actively supports his efforts to return to school and rebuild his life. She is one of the few people who understands his past and his struggles. The three girls, especially Jun, also form a significant bond with him. They look up to him as a mentor and a friend, and their unwavering belief in him gradually helps him rebuild his self-confidence. The online artist Kiriyume, who Kyō later discovers to be a girl named Yume Kiryu, also becomes a significant figure, as their long-standing online collaboration develops into a real-world connection.

Kyō's development is the core emotional arc of the series. He begins as a reclusive high schooler unable to leave his room, progresses to attending school again to ask for help promoting the girls' concert, and eventually takes on a more active role in managing the band and even resolving conflicts involving other characters. The process is not smooth; he experiences setbacks and moments of self-doubt, but each time he is pulled forward by his commitment to the girls and their shared love of music. By the end of the story, he has not only helped the band succeed but has also taken a significant step toward overcoming his own trauma.

In terms of notable abilities, Kyō is a competent guitarist and a skilled composer and arranger. He has a strong understanding of music production and is able to write songs that suit the girls' voices and style. He also demonstrates a practical ability to organize events, manage promotion, and handle the logistical challenges of putting on live performances. Perhaps more importantly, he possesses a natural ability to bring out the best in the people around him, a quality that is rooted in his own sensitivity and understanding of what it means to struggle with self-expression.