I am writing a novel which is about a naive, good-for-nothing boy who is also suffering from low self-esteem. One day, due to some events, he gets some special powers and is unwillingly forced into a war which he never wants to fight in, and faces many dark and harsh aspects of today's world (as I want story to be pretty dark).
While in difficult situations, he always seeks an easy way to escape, doesn't bother to face them, and is not willing to sacrifice himself for others, but at same time he can't stand the guilt of not saving others when he's able to do so.
I am also planning to make him fight with his sister, who is totally opposite to him, but he loves her more than anything - same with his sister, who also loves her brother more than anything. And his hero work is also shattering his own personal and professional life (he also realizes how dangerous he is and is harming his own health while becoming a hero), and he faces a severe emotional breakdown that he doesn't want to become a hero.
I am a bit confused about how to develop him with these events, because these things may push him down. Will the urge to gain respect and guilt of not saving people be enough, or should I add something extra, like a sense of responsibility towards his family or a desire to protect them? I want him to sacrifice his life for others.
What do you think I should do to develop him as a character? Should it be a single moment of realization, or a chain of events that changes his personality?
And how do I make him more likable? Should his end personality be serious but calm (which I think will be more suitable with his original personality), or a bit casual or funny with the same serious and mysterious personality when needed?