I am looking for a story about a guy that runs a store, or a shop and he's the long lost brother of the MC? I recall that he might be either a demon or running a store that was for demons ?
Sorry it's brief, but I can't seem to find it anywhere since the first time I saw it and did not write it down. It's not the pet shop of horrors, either.

Youkai Nii-san, I think.