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Here's another fanfiction idea: after Tony carries the nuke through the portal into space and destroys the Chitauri armada, the portal closes behind him. At the last moment before he runs out of air, he is captured and tortured by the Chitauri. Thanos allows this at first, but then hears of Tony's title and looks at the records of the Battle of New York. Thanos is impressed and he redeems him and gets him on his side (by brainwashing or persuasion, you decide) and Tony creates weapons, armor and spacecrafts. Thanos is more and more impressed by Tony and in the end they share a bed (maybe Thanos even makes him his queen ( ͡° ͜ʖ ͡°) ) After a few years they attack Earth to find the last Infinity Stones and Tony has to decide; stay with Thanos who truly loves and appreciates him or fight for the earth and save humanity.
I would be happy if someone would like to write a ff or use parts of it. But please give credits ^__^