Yashahime: Princess Half-Demon: Season 1, Episode 15

1 - 15: Farewell Under the Lunar Eclipse

Riku recalls events that took place beginning 18 years ago, when Inuyasha receives a new Black Pearl. 4 years later, on the night of Towa and Setsuna's birth, Inuyasha and Sesshomaru learn of a cataclysmic event that needs to be stopped.