Idea 1: When Loki comes through the portal into he Shield, he cries for help rather than try to fight. He warns them clearly of Thanos before his mind is taken over completely. What follows is the Avengers trying to rescue a mind controlled Loki as he tried to destroy everything against his will.
Idea #2: Loki stalks and kidnaps Pepper, then pretends to be her so that he can be with Tony in her place. (whether Tony and Pepper were even together or had already broken up, or how soon Tony catches on, may vary.)
Idea #3: Natasha knows that Tony is seeing Loki behind the teams back and even though Loki still regularly fights them, she makes a deal not to tell as long as he keeps her in the loop. Close in the loop. What follows is a sequence of Natasha being present or watching them while they go on dates or hangout. (And maybe one instance where she actually watches them have sex and they know she's there, or they decide to actively sex in front of her, either to bother her or try to goad her into joining because they're kinky bastards.)
Likes: A happy ending, fluff/romance, lady Loki, moments where Loki and Tony are vulnerable together, happiness (at some point that's not only the end, if such things are possible), an intimate moment or conversation.
Dislikes: Dub con, m preg, dark loki, asshole clint, overly stupid thor (not that he has to be smart...), fury being impossible, explicit torture or rape.