Before the events of the game, Tsubomi was the romantic partner of Lucifer, the Demon Lord of Makai. They conceived Setsuna, a Devil Child, together, but Lucifer returned to Makai shortly after. Tsubomi then courted the Archangel Michael and conceived Nagahisa, an Angel Child, but Michael too would depart for Makai. Tsubomi's sons, unaware they were actually half-brothers, were only told that their father mysteriously vanished. Tsubomi died of a terminal illness when Setsuna and Nagahisa were young, so they were left in the care of their aunt.
During Setsuna's journey through Makai in search of Nagahisa, he approaches a gravestone in Sand Land's graveyard. Tsubomi's spirit emerges from the grave, though she does admit to being Setsuna's mother, and tells him of his half-Demon nature. She also explains how Nagahisa is being guided by Angels throughout Makai, suggesting that Setsuna meets with Isis in her Pyramid. In doing so, Setsuna learns the spirit was in fact his mother, and that he and Nagahisa have different fathers.
Japanese