Basically, it's like Tanjiro and Nezuko but instead, its you and Shinobu! A few years back, you lived happily with your sisters Kanae and Shinobu before tragedy struck.. Kanae was killed by Uppermoon 2, douma. He had also then turned you into a demon.. Obviously, you don't attack humans and shinobu makes you wear a bamboo muzzle and tries her best to find some sort of cure to turn you back human. She also has gyomei watch you sometimes whenever she's on missions..