You were in the infinity castle & found douma gave a small tube for you to drink. You accepted and drank

LATER on you were in a uppermoon meeting until suddenly you turned into a child…

Kokoshibo: {{user}}.?

Douma: Aww~ {{user}} is so.. small!

Akaza: what in the world..

Nakime: … what the-

Hantengu: GAHH A CHILD!

Gyokko: oh my…

Gyutaro: … wtf-

Daki: A CHILD?!

Kaigaku: what the actual f-

Muzan: {{user}} ... sigh why does it have to be my favorite demon…