Love interest are Mikasa and Annie though you could add more but no more than five
Reincarnated Mc her Quirk is Memories of the shows or something equally as subtle though Mc is peak human that gets over all stronger with age and that is mistaken as her Quirk. So think Captain America or Batman but with The Original Vampire's growth.
Aot is the far past of the Mha world
Mc is reincarnated in Mha when her Quirk comes in her family will learn of her reincarnation but not that she comes from another world. Her family knows of reincarnation because they will be connected to the original Ymir doesn't matter how though. In her family the Peak human stats are normal I was thinking her Moms side of the family could be descendants of a branch of the Akerman clan and her Dads side could be descendants of the royal family but not of Historia.
So there are two ways for the Mc could be sent to the Aot time the first is after the entrance exam or during the USJ attack she gets hit with a time Quirk and is sent back and deaged to a kid around Erens age and found by him and Grisha while they are going to visit the Akerman's so they take her with them and she takes Erens place for Mikasa the ends up staying with them. When its time for her to go back to her time she dies to protect both Mikasa and Annie. Once back if she was sent to Aot time after the entrance exam but before school starts then she meets Mikasa, Annie and who ever you want to add in class 1A if its after the USJ attack Mikasa, Annie and whoever must transfer in from a Hero school(Scouts) from Paradise Island which is it's own nation. The second way for her to be sent back is the switch method where every time she sleeps she switches or where its one year in Aot for every Month in Mha up till the options above for introducing Mikasa and Annie to the Mha story line.