Nobody talking about how MC is leaving his students thinking he's dead, thinking they are safe, thinking they can trust "the kingdom".
He has a super mega tech level robot that could probably walk in there and save all his students with no problem, through force or stealth or just informing them to be careful and wait for opportunity.
But because that would be too easy author has MC go braindead, not even consider ways to save them other than building a robot harem.
How would collecting the robots even help anyway? Why would 7 robots work where 1 does not? These are super robots, they are either 1: too strong for numbers to matter or 2: an evenish match meaning they prb lose to numbers or 3: too weak to even matter... Or 4: JUST exactly so strong that only all 7 of them are enough to save the kids.
Number 4 doesn't seem very fucking likely does it? Unless you know you're in a retarded storybook that is.
Hell just telling the other non demon king kindoms (that seem to exist) about the kids would no doubt have them do their best to help him save them, just to protect themselves or in hopes of getting the massive war potential on their side.
Even if MC was scared of betrayal (he wouldn't be seeing how happy go lucky dumbshit he's been so far), he has massive war potential himself so the chances of anyone actually attempting betrayal are basically none without some author turning everyone braindead.
This plot is forced as fuuuuuck. Even more so than most isekai stories where MC having a vaccum brain is the norm.