Hayato Kirishima is the main male protagonist of the series. He is a first-year high school student who grew up in a rural village, leading to a somewhat sheltered understanding of the outside world. His early life in the countryside involved helping with physical labor, which has given him a well-trained and robust physique. Visually, Hayato is a young man of at least average height with spiky black hair and brown eyes.

Before moving to the city, Hayato befriended a child in his village whom he believed to be a boy. This friend was, in fact, a girl named Haruki Nikaido. After making a promise with her, Hayato relocated with his family to the city where Haruki lives. On his first day at his new high school, he immediately makes a positive impression on his classmates. A significant part of his early story involves his reunion with Haruki. Because he has always thought of that childhood friend as a boy, Hayato does not initially recognize that the girl he has encountered again is the same person from his past, a misunderstanding that causes Haruki considerable frustration. His role in the story is centered around this relationship, navigating the comedic and dramatic consequences of his mistaken perception.

Hayato has a few noted idiosyncrasies, including a hobby of collecting unusual rocks and stones. He is also described as being easily ticklish.