Fuyuhiko Kuzuryu starts out aggressive, vulgar, and distant due to his yakuza background and insecurities, but he undergoes significant character development, becoming a more sensitive, caring, and responsible individual who values friendship and atones for his past actions. He harbors deep insecurities about his youthful appearance, enjoys secret sweets, and is ashamed of his lack of traditional yakuza tattoos, but ultimately proves to have a strong moral compass and a pure heart.