give them the no fucks given attitude.
that is the secret ingredient no one knows about.
While all side characters are sad over first bandit death this guy is torturing the bandits so they tell him where they hid there gold.
{make him distribute the gold to the poor. So he doesn't come of as a prick but the guy who plays by end justifies the means.}
Don't make him self justified though. He should realize that these people had no choice but to turn to banditary and how sad it was.
He should know that it is a very fucked up situation but also that getting sad won't really help the situation and just break him.
SO better just laugh at the bullshit.
but also that there is no other choice . So instead of bitching about it he is going to whatever it takes to make it better while laughing at stupidity of the world instead of crying at it's evil .
Make him the protagonist who uses lot of black comedy.
Make them monologue a little about society (how no one is there true self everyone is wearing a mask of fake politeness and just quietly suffering and then dying. Worst of all they are letting this continue)[you live in japan you know what i am talking about ]
Imagine you found yourself Trapped in Another World, far removed from everything you know with no promise you could ever go back. And just as you started to come to grips with that, you discovered you were The Chosen One and that this world …
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Make them laugh with a slight maniacal tint at the shit life throws at them .
EDIT: I Just realized make him a realistic average teenager. Don't make him a Japanese MC