I don't think fix is the right word. They're merely brought to heel.

( He thinks of Kuchisake-Onna and her desperate violence, and the snapping of the dragon's jaws as he sent her Fushiguro Toji's way. No, fix isn't right. And yet rainbow dragon nudges her snout against Jinx's fingertips, careful. He does have kinder curses, just like he has kinder moments. )

She's docile because I want her to be. I was fifteen when I found her. Any fifteen year old comes across a dragon, they're going to want it to be fun, mm?