Masaru needs to find a way to power grind skill points. Keys to do so is tell allies(harem) about power and then help him find a collection of like 30 skills he can get one level in really easy. After the cooldown for skill reset is done he hits it and gains 30 skill points, then add those points to useful things. Repeat for a year and have all battle skills maxed out. Help wifes do the same thing and pow, demon slayer squad formed.