Like My Very Own Blood
Minister Riddle won his election in part because he took the extremely charitable path of adopting a war orphan—Harry Potter, the child of a historically Light family—and raising the boy as his own. It was an investment worth making… or it had been, until his quiet, clever son grew into a brilliant, scheming Omega determined to seduce his adoptive father by any means necessary.
Or: Harry out-Slytherins the ultimate Slytherin, and Tom’s absentee parenting comes back to bite him on the ass.
(Or make him bite Harry on the ass. Or. Whatever. It’s all very bad-wrong and you should probably avoid this story unless you are morally bankrupt. Like me.)