Thanks for the chapter!
While being able to use a flush toilet with soft toilet paper is levels above using a hole in the ground/seat that just collects with scratchy leaves, I don't see why he didn't talk to numerous craftsmen and BUILD ONE. Heck, could probably make a better or portable one with magic. Like the MC in Gun Ota... There were no toilets so he not only created one, but also portable fully functioning toilets as well. Ambushing and killing his comrades however was way over the line. Considering his combat power why didn't he just tell them were going to take route X in the morning, wait for them to fall asleep, then take all the food, the map, enough money so they're able to return home but not follow him at least for a while, and take route Y before they can wake up. Don't know enough about what they were criticizing him about so can't judge based only on his side of things. As for hellish training didn't see training so can't judge whether really was hellish for no reason or just extremely strict to hammer into him what needs to know so can survive battles as can't argue that the results of such allowed him to kill the Demon King solo. While agree that kidnapping him, forcing him into life or death battles, forcing grueling (possibly hellish) training which may or may not have been unnecessarily rushed, and stating can't go home until defeats their enemy the Demon King. After all, is there a reason why has to be a summoned person to become a hero instead of training skilled countrymen so have several or groups who can kill the Demon King, or were politics involved? Politics such as wanting to summon a hero so no big loss if dies and if succeeds will be sent home rather than worrying about whether or not the power to take down the Demon King will be aimed their way or the country. In any case, agree his personality is coming across as very bitter, selfish, with a strong refusal to refute or take responsibility for his own actions, especially when it resulted in harming or killing others. Granted Sword Princess over-reacted with lethal force due to him seeing her naked considering she left the door open before stripping and should've covered herself while telling him to close the door and stop looking.
BTW Shouldn't the elf be Elf Queen or Elf Princess instead of Elf King since the elf looks like a female instead of a male?