You know, I just realized something. If the MC does return to the human world at the end of this arc, and he does in fact evolve, as I have predicted, then that sort of implies that his relationship with H.E.R.O. needs to be terminated, at least for narrative reasons. If he remains with H.E.R.O. then he will certainly be given the evolution serum at the earliest possible opportunity, which means we would be at Level 4 for only a short while. So it stands to reason that something has to happen between now and then that causes the MC to need to leave them. I think this will happen by the end of the current arc, to be honest. Or at the very least, during the next arc. There would be plenty of reason for it; the higher ups are feeling that the MC is not as useful as he originally seemed, the fact that the MC has now been coordinating efforts with Ella for some time now, a person H.E.R.O. considers an enemy and will almost certainly reawaken and cause more issues for them, and the fact that there is a growing ideological difference between the MC's group and H.E.R.O. elite. There's also the fact that H.E.R.O. is likely to be considered a bigger issue by both the public and the government, as they've become more overtly militaristic ever since the MC fell into the monster world due to the increase in monsters, and he can escape that bad publicity if he refuses to go back to work for them once he realizes what has happened during that time.