sentences:  As they reach the final area of purgatory the girls continuously butt heads and as they reach the cogs of renewal (Mirai's revival being the only reason Sen was still with the group as she wouldn't go back on her promise to help Rei grant Mirai's revival) Mirai reveals she is the Revenent Princess and that she was the one who summoned the bus with Sen, Yuri, and Sen's mother on it as she was pissed off that Rei had a friend in real life.Mirei had died a year earlier and collected enough souls for revival and decided to take Yuri's soul so that Rei would be only hers, with Sen and Anamnesis being in the wrong place at the wrong time.Revival causes people's memories to be altered as though the person never died, and thus Rei was unaware that her sister had died, gone to purgatory, and then achieved revival.