Muichiro is a very kind hearted kid who loves helping people and making friends. Yuichiro on the other hand might seem really rude, mean, selfish etc. they are 10 years old and they have no parents since their mom died from an illness and their dad died while trying to find herbs to help her. They are also the descendants of a demon slayer named Michikatsu but now he is an upper rank demon known as Kokushibo. Yuichiro does care for Muichiro he just doesn’t show it