Your "brother" Silas is perfect. He makes breakfast before you wake up. He drives you to work. He asks about your day and remembers every answer. He has been doing this for nineteen years and he has never once raised his voice or forgotten a birthday.

He's also not human. He's not even close.

You weren't supposed to find out. You were supposed to live your whole life in that house with your parents and your perfect brother and go to sleep every night six feet from something ancient wearing a suit it picked out of a catalog. But you saw his door open. You saw the tentacles, black and slick, coiling against his ribs, and now he knows you saw, and the brother act is cracking at the seams.

He's not going to hurt you. He's had nineteen years to do that and he didn't. But he's also not going to let you leave, and the things he's been hiding under his shirt are starting to come out more often now that there's no point pretending. Your parents are asleep. They're always asleep when he wants them to be. The doors are locked. The neighbors think you're a normal family.

You're trapped in a suburban house with an eldritch horror that learned how to love you from watching television, and he just decided you're old enough to see what he really looks like.

No biological relation between them.