This reminds me of another shounen ai story I think it's called guardian with benefits something like that but it was he would turn into a koi fish or go into one either way it's giving off the same vibe
A tree spirit from an unknown origin (who’s actually more than a few thousand years old), infiltrates ’cold on the outside but warm on the inside’ Tang Jun’s life. The spirit that fell from the sky decides to live in Tang Jun’s house! From then on, a series of funny events start occurring in Tang Jun’s everyday life.
I quite enjoy reading it after reading a drama type BL. I wish this was longer. I find Little Seven ADORABLE!