Near the end of the anime, Tomoe joins the dark side to be able to kill Arika with her own hands, but she loses to Arika and is reported as dead (even if she is alive...). Tomoe returns at the next season (Mai Otome Zwei) as a mayor's wife. Yes, she married him so she would be rich and have power to continue trying to kill Arika. She tries again and fails again, this time probably finally giving up.