 The anime's second season reveals that Yougetsu is actually another one of the Eight Sages, Byakuya (the Sage of Haku, the White Immortal).When Doshuu found Eigetsu, Yougetsu saved the child's life by strengthening his dying soul and granting him twenty more years of life, but after that, Eigetsu himself would die and Yougetsu would live on in his body.Later, Doshū became gravely ill, so that Eigetsu willingly surrendered ten of those years to Yougetsu in order to extend his foster-father's life.