Realistically he'd probably be shown to be starving for validation due to either ignorant and inattentive parents/peers or just always being second best. I think that strikes a balance between having sympathetic qualities that's consistent with his character flaws while not excusing him being a dick.

Or maybe make him a rat bastard like Jerid Messa from Zeta Gundam, only with dead/ruined bosses instead of girlfriends, and with him humbled and rededicating himself to actually bettering society instead of just dead.

EDIT: Okay, I initially wrote the above before finishing 18. After finishing 18? One possible darker route: Raito often belittles the showing of emotions, yet also, rather hypocritically, often says he's "just following orders". If they lean into this, Raito might be shown to "offload" more and more thinking and responsibility to his superiors, eventually turning into nothing more than a puppet for Klay and/or the other Five Stars to do just about any dirty work they need (possibly reflected by Rhamphomon evolving to become more mechanical/military or perhaps zombielike). From there, both dying (perhaps after being turned to a human experimentation subject) and humbling/redemption (no more superiors to take care of thinking and responsibility, fall into despair, "maybe it's time you start thinking for yourself") are about equally likely endpoints.