Yaoi manga. I'm not sure if it's a oneshot in a collection or a series.

I remember there was a lake or a pond, but the setting is in a city. The character somehow fell in and met the spirit or demon or merman who lives there. And another thing I remember is that the guy ended up feeding from the merman's body, and the merman ate other people.

Please, please, if you have any idea which manga it is tell me Dx I've been thinking about it for days now.

Yume ni Tobu Tori - chapter 2?

Thanks, that's the one