I'm thinking both the MC and Graham were reborn but just like the MC, Graham has a plan on how to stay together.
Ooooo I like this idea
what if instead of being reborn the hero is just chosen by whoever is with the MC at the time, and the dark haired one is the one who pics them because he wants MC [Jun] so he tries to break her engagements off and get her to himself , and the memories the MC can't remember are memories of him trying to get the MC to his side[fall for him?]
Oh yeah, I like the idea of the hero secretly remembering the past lives, every time the demon king has made it that he’s been with someone else extra.
but I also think that that theory, since the demon king seems more of a main character, is more likely
Except, what you and Mavikelebek below seem to be forgetting is that the DK seems to be happier with the turn of events that are happening at present rather than the ones that happened in her previous lives.
"Smh my head"