Yoshitatsu Kawai is Honoka Kawai's father, divorced from his wife and sharing a home with his daughter. He works as a famous novelist, a profession leaving him constantly exhausted and contributing to his perpetually tired appearance. Despite this fatigue, he demonstrates kindness and thoughtfulness as a parent.

He shares a significant past with the Sawatari family, being childhood friends with both Ryo Sawatari and Haruka Sawatari. During their school years, Yoshitatsu harbored romantic feelings for Haruka, a history adding complexity to their ongoing adult relationships.

A notable aspect of his involvement centers on his possession of a core component of The February Dawn. The exact reason for him having this alien artifact remains unexplained. The February Dawn is an artificial intelligence originating from an unmanned extraterrestrial probe that crashed on Earth in 2022 and later camouflaged itself within the apartment complex where the characters reside.