Looking for a BL

I remember reading a BL where the main couple was a human guy and a clam spirit. The clam spirit finds the other guy and tells him that he has to make a deal with him that would keep him on Earth. The guy refuses. There's also some backstory that shows the human as a child by the seashore and finding the clam spirit in his small form inside a clam. The current 'antagonist' is some type of sea serpent spirit. I remember random parts such as:

1. When the clam spirit uses too much magic he shrinks down and has to rest inside a clam.
2. The clam spirit has some type of brother/son that, when the antagonist trys to take the clam spirit, tells the serpent he'll take his place and spend time with him instead. The smaller clam spirit also calls the human "Mom".
3. The clam begins to doubt that the human is the one he saw as a child because the human's attitude is colder.
3. The serpent gives the human some type of poison and the clam has to come back and help.

I'm not sure whether the story was on this website or not but if anyone knows the title it would be greatly apreciated.