Complex sentence: Bellamy's character is one that is arrogant, violent and vain, but significantly humbled when facing more powerful foes, since he revealed to his superior, who is a Shichibukai, that he only engages in fights that he knows he can win.
Split into simpler sentences: Bellamy's character is one that is arrogant, violent and vain. But significantly humbled when facing more powerful foes, since he revealed to his superior, who is a Shichibukai, that he only engages in fights that he knows he can win.