Yōhei Yamada, a cheerful and obedient young boy, discovers Chi—a small grey and white kitten—lost and separated from her mother and siblings. With his mother, Miwa Yamada, he rescues the helpless kitten and brings her to their home. Despite living in a pet-prohibited housing complex, which initially prompts efforts to rehome Chi, the family ultimately decides to keep her.

Yōhei demonstrates consistent kindness toward Chi, sharing responsibility with his parents as she adapts to household rules and navigates new experiences. His mother, a housewife, primarily cares for him and Chi at home, while his father works as a graphic designer, often remotely. Yōhei's interests include a fondness for toy trains.

In later storylines like *Chi's Sweet Summer Vacation*, Yōhei remains a caring presence in Chi’s life. He joins his family and Chi on a trip to Okinawa, encountering new characters including a girl named Aina and other cats, while continuing to participate in Chi's daily adventures and discoveries.