Hiro Shirosaki is an eighteen-year-old third-year high school student and one of the main characters in the story. He comes from a family with strong local ties, as his grandfather, Matasaburou Shirosaki, owns and operates the Kazemichi cafe. This cafe serves as the central gathering spot for his close-knit group of friends, where Hiro also works as a waiter. He lives with his older sister, Momo Shirosaki, who also works at the cafe, and the two share a relationship characterized by frequent, good-natured bickering. He has been a close friend of Yukinari Imi since their middle school days.

In terms of personality, Hiro is consistently cheerful and is often seen with a smile. He possesses a light-hearted and optimistic outlook on life, frequently encouraging his friends to look forward to the future instead of dreading it. He is a loyal and caring friend, always willing to look out for others. This is demonstrated when he agrees to adopt a chicken at the request of Touko Fukami and when he makes the effort to frequently visit Sachi Nagamiya during her stays in the hospital. However, he can be somewhat oblivious, with his friends noting that he has difficulty reading the mood of a room, particularly in social situations involving girls.

Hiro's primary motivation throughout the story revolves around his romantic feelings for Sachi Nagamiya. He is earnest in his pursuit of her, though his attempts are often awkward and do not go as planned. When Sachi is hospitalized for medical checkups, he visits her every day, putting considerable effort into finding ways to connect with her. He begins reading books so they will have topics to discuss, and he specifically addresses her by her first name, "Sachi," a sign of his special affection, while using more formal honorifics for other female friends like Touko and Yanagi. His hobby is mountain climbing, a passion he uses to plan trips and create opportunities for his friends to spend time together.

His role in the friend group is that of a stable and energetic core member who helps maintain a positive atmosphere. He is notably one of the few in the group, along with Yanagi Takayama, who initially thinks positively of the newcomer Kakeru Okikura. Hiro's character development is tied directly to his relationship with Sachi. While he is persistent and devoted, he experiences significant emotional conflict upon discovering that Sachi may have been using his feelings to interfere in the relationship between Touko and Kakeru. This realization leaves him deeply confused and hurt, forcing him to confront the complexity of the situation and his own vulnerability. His journey is one of navigating unrequited, or at least complicated, affection while trying to maintain his supportive and upbeat nature.