So I have started to write a story, it features 3 male characters and a single female character. Their names are Baldur, Cyrus, Vidar, and Aer( the first three are male the last one is female) later more characters will be introduced. My question is I want each one to grow up and the main character (Baldur) I want to become merciless, how would I have him still be realistic and relatable. He has seen things that have changed him. Vidar is the clever rogue he has a knack for games of both mind and sleight of hand. Eventually he will become a great general. The last male character Cyrus is the nerdy kid who constantly reading. I want him to be throwing out facts constantly and eventually become a great user of the power( magicish) how do I evolve these characters slowly yet constantly? Make their change of hearts natural ?