Rindou Ranmaru's Mother

Rindou's Mother was a character that didn't appear during the series due to having passed away sometime beforehand. She did however have her design shown when she was younger and was briefly talked about by the author in the Volume 10 extra chapter Q&A when someone asked him about why Rindou's hat had a rip in the back of it. It was explained that the hat used to belong to Rindou's father, who in his youth was an unrivalled leader of a young band of fighters and had received the damage when he finally met his even match, that opponent being Rindou's future mother.