Genshin Impact, yandere, system and isekai... what could go wrong?

The isekai that everyone is tired of ends up in Genshin Impact after colliding with a truck. There is no backstory for the main character, except that he was a passionate fan of the game and had a good understanding of the lore.
And so, it would seem, you ended up in Teyvat, you were given a system and rejoice, and collect yourself a harem of many girls and guys. But the system turned out to have a small "surprise," and the universe was also not quite the same, the familiar Genshin Impact universe.