Big Spoiler
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He was someone who took good care of Felix and supported him, when they first met. But then that guy's mother told him that Felix is the real child of his father, while he himself is not related by blood. Due to this the mother told him to get rid of Felix and his family. Starting from there their relationship becomes twisted and the red head threatens to hurt Felix's mom and sister, if he won't do what he tells him to. Like that Felix did what that guy told him and started to work for Gio. So all in all a long time ago that guy was like a big brother to Felix, but now Felix hates him, while that guy is unhealthily obsessed with him.
whats the red head dude to felix? im only on chapter 27 but pls spoil me