The Odinsons are normal people who live in Chicago. They can't have a second child and adopt Loki from Russia. He was born with fetal alcohol syndrome and the older he gets, the more out of control he becomes. When his aging parents can't deal with him anymore and decide to institutionalize him, Thor promises to take over, and that they can leave Loki to him after they move to Florida. What his parents don't know is that to keep others safe from Loki, Thor has build a dungeon under his bookshop, outfitted with all comforts but nothing dangerous, and if necessary he can put Loki in bondage when he has a meltdown. While at first there is nothing funny going on, he has always been fascinated with how different Loki looks from him, with how pretty he is in spite of his relentlessly psychopathic ways. In a bid to escape, Loki notices, and tries to seduce him. Loki succeeds in the latter, repeatedly, but not the first.

Bonus if Thor angsts a great deal about hurting his poor baby brother and betraying the trust his parents put in him. Extra bonus if Loki enjoys Thor's angsting. Extra extra bonus if Thor is engaged to Jane Foster but has to break it off to protect his secret. Loki should be at least 17/18, and Thor several years older, but not over 30, young enough to have lived at home while Loki grew up.

No torture, no rape, no scat, no disciplining other than restraints, and no redeemed!Loki please, he's genuinely not aware that the things he does and say are unacceptable, and he never will be.