When she was a young girl, Towa suffered from a deadly illness. Her twin sister, Sawa, gave Towa the blood of a mermaid, which cured her but left her with a deformed arm resembling that of a Lost Soul and turned her hair pure white. Though she didn't age externally, internally she remained the same. Upon discovering what Sawa had done, Towa's father locked her in a cell beneath the house, never to be released. Meanwhile, Sawa went on to live a normal life, marrying and having children. Towa, isolated from the world, found solace only with her fiancé, Dr. Shiina. Her deformed arm caused her immense pain, leading her to request that Dr. Shiina dissect the arms of deceased girls and reattach them to her. However, each new arm also became deformed, worsening her agony.
Towa nearly lost hope until Mana died in a car accident. Dr. Shiina was about to remove Mana's arm when she suddenly revived. Towa then devised a plan: she would transfer her consciousness into Mana's body unless Sawa revealed the location of the mermaid mound. Although Towa showed some affection for Mana, it was unclear whether this stemmed from her desire for an immortal body or other reasons. After finding the mermaid, Towa intended to give its flesh to Sawa as part of her revenge, but Sawa died of a heart attack before this could happen, leaving Towa with no purpose. In the end, Towa chose to join her sister in death.
