Muzan and Kagaya is sblings, Muzan is 15 and Kagaya is 1. They were both born ill, but loved to play, Muzan was very smart, but had troubles with his health and got sick often, but he was very smart for his age, Kagaya however, was autistic, he couldn't speak yet.. and showed what he wanted to with body language and was developing a bit slower, but he was observant, and smart in his own way.

It's summer break and Muzan put Kagaya on a play mat