What BL was this?

I started reading this BL around 1-2 years ago, I think...? the only thing I can remember is that the MC was a university student and the ML showed up suddenly and they were apperantely family-related, according to the ML. But the ML was very weird. The people around the MC saw the ML as a different appearance than the MC could see (creepy).

I don't even know if I even liked it but it's bugging me that I never finished it and now I can't find it