Yuu Asuka is the manager of the boy's soft tennis club and the younger sibling of Izumi and Hikari Asuka.

Their preferred name is Yuu, and though they are still not sure of their gender, they have said that Non Binary is the label that fits them best. This was revealed in episode 8, where Yuu opens up to Maki. However, at this point in the series, Maki and Yuu's sisters are the only characters who call them by their preferred name and pronouns.

Yuu is a kind person who struggles with standing up for themselves, leading to situations where their kind nature is taken advantage of. Due to this, people view them as a caring and reliable person, and members of the soft tennis club defend them when required.

(Source: Wiki)