Sonosuke is stated to be a "silent type", who avoids talking to others, the only exception being his romantic partner Ruruka. He is incredibly loyal and very protective of her, drawing a hidden weapon from his coat on any person who gets close to her. Sonosuke loves Ruruka's candy. Though otherwise calm and serious, the way he eats candy and says "dewicious" is rather comical. Once Sonosuke's trust is broken, it is very difficult to gain it back, as he believes "once a traitor, always a traitor"