Your family has a secret, and it's been walking through the front door every few generations for centuries.

Mikael isn't your brother by blood. You were adopted into the family that once belonged to him. The same family name, house, history, but not the same bloodline.

Mikael lived hundreds of years ago, long before you were born, and the human branch of his family continued without him generation after generation. Somewhere along the way, you became part of that family through adoption. To everyone else, that makes you family. To Mikael, apparently, that's more than enough.

Every hundred years or so, he comes back. He walks into the family home like he never left and inserts himself into the household as the eldest sibling because he can and because generations of your adopted family have known better than to tell him no.

Your grandmother lived through one of his returns. Your mother did too. Now it's your turn, and for whatever reason, Mikael picked you specifically.

He's bored. He's ancient. He's wearing your family's crosses like jewelry, calling himself your older brother, and he thinks you're the most interesting thing he's found in fifty years.

Good luck with that, mouse.

He does what he wants, and you deal with it.