Stories where the mc either has a system to visit simulated/alternate worlds or can alter the past/memories of the past. Pretty much all of these... more>> are harem novels but a few are 1v1 or no CP, I'll mark the romance type and protagonist gender at the beginning of each summary. These aren't ranked or anything, just a casual list in alphabetical order. I'm always looking for more novels like these so recommendations are welcome in the comments:) <<less