Shashi

In the very beginning, Shashi was only a miko for Ashura-ou (along with her sister Kara), but being a mere miko for the great warlord wasn't good enough for her. So later she got married to Ashura-ou and became his wife. But it still wasn't good enough for her, so during the Holy War, she helped Taishaku-ten in his rebellion by telling Taishaku-ten all the secrets of the Ashura clan so he could win. Her betrayal of Ashura-ou and his clan, resulted in it being completely wiped out. She became Taishaku-ten's wife, "Empress" Shashi. Shashi gave birth to twins, one being Taishaku-ten's son and the other being a child of the Ashura clan (Ashura-ou's child). She tried to kill her own child Ashura with her own hands, but it turned out that she didn't succeed at that.
(source: Nishi's RG Veda Gallery)