I'm deeply sure, that heroes can't live for long in really dark, hostile worlds, if they are written realistically. They are too inflexible for surviving in tough, morally complicated situations. So all possible opportunities to save them, retaining their heroic dignity in the same time, are artificial and boring. They will die in the first such a situation, if only author will not make them absurdly overpowered or will not constantly use Deus ex Machina and other artificial methods to save them.
And, since I like complicated settings and situations, my main characters just can't be heroes. Besides... most of the heroes I've seen themselves look boring and unrealistic for me anyway. I feel irritation for them more often, than empathy. So I feel no desire to make them main characters.
Main characters in my comics are something in between anti-heroes and villain protagonists ( yes, my choice was between these categories, not between anti-heroes and heroes
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A year ago, when I just started to planning all of this, I wanted to make them pure "villain protagonists", who have bloodthirst and lust, but no empathy or mercy and are pure egoists. So I wanted to implement "all shades of black" trope.
But in the process of refining plot and setting, I've slowly walked away from it a bit. I've realised, that the plot itself pushes them to develop human feelings in some situations, so they can't being kept "black" without feeling artificial. Moreover, if I will allow them to be "dark grey" instead of "black", it will make them more interesting. So, I've decided to let them have these feelings.