Looking for a yaoi

Hello !

I've been looking for a yaoi I read some time ago. It's a school setting, but in a fantasy world. There are "heroes" with special traits (the hero is like a lion on fire if I remember well). When he was young, he saved some girl who has mermaid traits. He's been wanting to meet her again, when he discovers that the pretty mermaid was in fact a guy at his school

Thank you in advance ~