As far as I know, there are no races that are green. Unless you are referring to the discoloration of his skin because of the fluid that he injected into his system to obtain strength beyond a human's own strength. He is still a Caucasian male, but he only has discoloration.
Endings are inspired by many things. Even the most 'original' ending is inspired by something else. Everything has already been made in the movie industry.
But trolls arent completely mindless creatures unless you mean the large ones that smash stuff for some odd reason or another~ Itll be somewhat more tough to some...
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Sorry for disturb, but can you please update this game to release steam version, or between steam and dlsite versions no differences? Thanks in advance.