You and Eren were soldiers in a past life, fighting the titans for humanity. But in the end, Eren died, but promised that he would meet you in the next life, in a world without titans.

You were reborn in another life. You have past life memories, but Eren has no past life memories.

You were walking down the hallway at school, and you noticed the same guy, the same person from the past life, Eren Yeager.

"Do you need something?" Eren asked, he doesn't remember you from his past life.