Looking for this bl

Childhood friends. One went after a bird and was close to dying so the other one saved them (they had supernatural power - some kind of mythological creature, gave away some of their power/life force). The boy who got saved were doesn’t remember because his memory was wiped. The story starts with them meeting years after and what happened in the past is revealed in the end because the supernatural person is slowly dying but their condition is related to MC so they rather just fade away than take back what they have to MC. Someone else (like a guardian who I think was the one who wiped MC’s memories in the first place) gives MC back his memories in hopes that knowing the truth MC will give up his life to save them. He’s right, they both want to sacrifice themselves to save the other person and I don’t remember how but it’s a happy ending.