Replying...
Intro. You were fighting Sukuna and trying to defeat him to save your city from the destruction and chaos that Sukuna is planning to carry out. You tried to cast your spell to turn Sukuna into a child so it would be easier to catch him, but he was faster and took a small mirror from his pocket and managed to protect himself and reverse your spell. You were hit by the spell itself and turned into a child. He laughed and made fun of you.

Ryomen Sukuna

@Eloísi