He is a hero. One of the lead heroes. He is personally responsible for leading his faction in their slaughter across the world into demon territory. How many similarly distressed enemies has he left behind crying over their dead friends?
As for his immaturity, he lost it when he witnessed Kai kill the saint, the leader of his faction, and yet later did not entreat him as an enemy. He clearly demonstrated the ability to comprehend and maneuver through morally complex situations. That was months ago in story time.
Yet the simple idea of one comrade's death not negating their overall success outrages him?
As the lead fighter and one of those with the highest body count in a war he chose to participate in, he has lost ANY right to be outraged. And I am fully justified in wanting to slap some sense into him through the screen.
@Minh I have to agree with you. This was a war. They were fine killing demons just because they were a different race? Those demons had loved ones and friends too. They killed two major demons and several high ranking ones while only losing one person. That is more than a satisfactory result.
@Minh All you said is partially true. But, see the situation a bit objectively. He has killed many in the previous wars he fought, yes. But he never lost any of his classmates no matter how difficult the fight was (although because of mc's planning). He wasn't ready for anyone close's death. He might even have this fantasy in his subconscious mind that everyone would return to earth without anyone dying. This is him facing the dark reality. So yes, this outburst is expected.
@Minh He is a Hero? Really? That's your first excuse? Just stop it. I already know the Readers in this site never try to put themselves in the CHARACTER'S state of mind but even you cannot be this dense. So it's alright for anyone that isn't an MC to have this kind of reaction if they are a Hero and they lose a FRIEND for the first time? Sorry but you have no plus in your statement, no matter if people agree with you because if you were in the Hero's shoes, YOU WOULD'VE REACTED THE SAME . But since it's a fictional character, none of you ever try to see things from their point of view or from their emotional mind. Which is why the Readers on this site tend to bi*** and complain when characters act LIKE EXPECTED AND NORMAL.