@NamelessSoldier:
Wasn't it, from an earlier chapter, that he has weird prophetic powers and likes to write down stuff that
could happen in the future—which is ultimately how we, in some weird time loop, end up with his time-traveled Earth-reincarnated self writing the plot for the game she played in her past life, which is the explanation for what's ultimately going on and how this wasn't actually a game world?
Which was a bit contrived and convoluted. But I honestly appreciated the author taking the time and effort to not just hand-wave the practical existential conundrum inherent in the whole "we're in a game setting somehow" stuff.