"What would you do if one day your boyfriend suddenly transformed into a girl?"

One day, the protagonist is the girlfriend of a boyfriend who has undergone a TS (gender transformation) and become a girl. Since it's a pure love story, they're basically being lovey-dovey. Even the serious parts recover through being lovey-dovey. In the end, the girlfriend pushes the boyfriend into becoming a girl and makes him meow like a cat. That's the kind of story it is.