All the one-sided Elsanna fics have Elsa being the one in love, with Anna not loving her back. What if it was the other way around?
Prompt Idea #5 - Anna and Kristoff are happily married (because I think Anna learned her lesson and took it slow, she wouldn't have married him unless they had true love). However, Anna can't stop being attracted to her older sister, who seems completely oblivious. She takes her marriage vows seriously and keeps her feelings a secret, to protect both of the people she loves.
FIVE ways this could end...
5a) Elsa only loves Anna as a sister, and is horrified to find out Anna's un-sisterly feelings when Anna gets a little too drunk one night. Anna is equally horrified upon realizing she let out her secret. The revelation ruins the sisters' relationship making them both terribly awkward and wishing they could go back to being very close sisters again, but they can't. Finally, Elsa can't stand seeing her beloved sister unhappy, and makes an ice golem of herself for Anna to 'play' with. The problem is solved – until one day Kristoff walks in on Anna using the golem… (oh yeah, remember Kristoff's fascination with perfect flawless ice? Go figure)
5b) Elsa does reciprocate Anna's attraction, and unable to resist each other, they start a scorching affair. Somehow, against all odds, Anna manages to cheat on Kristoff with Elsa for decades without getting caught and continues to be a good wife to Kristoff and mother to their child (the heir to the throne). Kristoff is shocked but surprisingly not angry when he finds out he's been cuckolded, and even pleads on Anna's behalf when she is condemned to hell for her sinful life. Unfortunately, true love is not a defense according to God's word.
5c) Anna (despite trying not to) cheats on Kristoff with Elsa. Kristoff cheats on Anna with Sven. When they find out, none of them know whether to laugh, cry, or scream.
5d) Elsa doesn't want to admit her attraction to Anna, even after Anna confesses her side of it. So she pretends to feel only sisterly and makes Anna an ice golem of herself so that she doesn't have to dirty her hands. Secretly, Elsa also makes an ice golem of Anna for her own use. One day, the castle is being renovated and the sisters' bedrooms have to be temporarily cleared out. Both sisters stash their golems in the same dark storage room without noticing the one that's already there. The golems are accidentally activated, discover each other, and act exactly the way they were made to. Someone walks in on them. Drama happens.
5e) Elsa secretly reciprocates Anna's attraction but they never find out about each other until they die and go before Christ for their final judgment. They are condemned to hell despite not acting on their sinful attraction because "if you look at someone lustfully you have already committed adultery in your heart". Elsa and Anna stare at each other in disbelief, almost wishing they'd gone for it, since their lifetime of self-restraint didn't end up saving them from hell anyways!