There is a minor side-character in the story she at some point meets that didn't appear in the game. He seems to be able to see different possibilities of the current timeline...not the future, just how the present could've gone differently. He writes them down and MC finds that out through accident. She sees the possibility that the game took where she is a villain and the heroine ends up with the ML (something she deviated from) so she thought he was a reincarnator too...but happens to be not. She asks him about yanderes (cause that's the main theme of the story) and he doesn't know of it, but gets way too into the idea of it and she ends up realizing that he might be the one who reincarnates into her original world later on and regains his memory like her then makes the game that she played. As to her theory of how they regain their memory, it's by coming across something that they've known in their previous life. For her it was the events of the game that triggered her memory, and for him it's the existence of the yandere troupe in modern stories that he heard from the MC. So it's not really a game world, but a game based around a different world. (Anyway, he actually had his own ships in the visions he used to see so he didn't have the original events be a part of one of the game's routes. He also didn't include himself in it. And although everybody is not a yandere, he turned them all into one cause he really likes that troupe...which ended up causing the MC massive paranoia when she thought she was in a world filled with yanderes. lol)