Mother is a supernatural entity who serves as one of the two antagonists of Forbidden Siren 2. Trapped in the Underworld, her aim is to be free before wreaking havoc on the human world and ruling it.
Mother and Otoshigo were created when the Earth was; before it, there were many dark creatures. When God created light, the creatures combined into one entity and split into two; one was eventually trapped in a cave in Yamijima, and the other went into the ocean, waiting for its mate. The trapped one became known as Mother, while the sea-dwelling one is named Otoshigo. Mother remained trapped on the island in the Underworld for countless centuries, and Otoshigo spends millenia searching for her. Seven seals surround her location, preventing her from getting out.
During her imprisonment, Mother uses entities created by her to try and free her. These creatures, avatars, would go out and manipulate a male into breaking the seals.
In 1976, Mother creates an avatar, Kanae, based on the deceased wife of Ryuhei Mikami, in order to manipulate Ryuhei's young son, Shu Mikami, into removing the seals. However, the town fishermen catch Kanae in the act of killing Ryuhei, leading to Kanae and Shu falling into the sea. Mother, angered by the interference of the humans, unleashes a red tsunami that covers the island, sending the inhabitants into an alternate dimension that also folds time on the island.
Years later, Mother creates another avatar, Ryuko, who goes to Tokyo to find a man to manipulate. Unexpectedly, Ryuko finds herself immersed in human life and abandons her objective. Two years later, the avatar Yuri is made, and finds and murders Ryuko for disobeying her nature. Yuri makes her way to Yamijima, where she eventually comes across Mamoru Itsuki and is successful in making him break the seven seals, creating a portal to the Underworld.
Mamoru and Yuri go into the Underworld, where Yuri reveals her true nature by removing her shirt and revealing Mother's face on a blank chest and stomach, shocking Mamoru. Mother summons a large headless jacket-like body that envelopes Yuri/Mother, giving the creature a new body with Yuri's face. Her new form is witnessed by Soji Abe, Ikuko Kifune and Akiko Kiyota; Soji sees her as Ryuko, due to the resemblance between avatars, but he dismisses Mother as being her. Mamoru is drawn to Mother through hypnosis, though the timely intervention of Ikuko causes Mother enough pain to release him. Shu, on the other hand, sees the deity as Kanae, and happily walks to her before realising at the last second that she is absorbing him, allowing her to birth the Yamirei.
The portal to the Underworld is closed by Mamoru and Ikuko, thus preventing Mother and countless Yamirei from entering the alternate Yamijima reality, save for the many Yamirei that have entered the realm.
Mother is able to escape the Underworld and plans to use the Spider's Thread, a gigantic tower, to cross over to the real world via a portal in the sky intercrossing both realities. She aims to do this before the fake Yamijima reality collapses around her. Making her way up the tower, she inadvertantly knocks an Otoshigo-possessed Ichiko Yaguri off the Thread, and comes upon Mamoru and Ikuko. Wishing for them to be gone, she sends them into a realm of her own creation, where she fights them.
Ayiko - possessed by Kanae - finds herself in this plane, looking for Shu, who is also there as a spirit looking for Kanae while surveying the fight. Ayiko, able to regain some control, stabs herself with the Annaki Remains she has with her, which kills her and hurts Mother. This causes the Annaki Remains Mamoru and Ikuko have to transform into swords. Armed with their new weapons, the two stab Mother, killing her.
Upon her defeat, the sound of a siren blazes as a red wave washes over Mamoru and Ikuko, sending them to a reality where Mother never existed. Mamoru wakes up on the shore of the island before reuniting with Ikuko, who is unconscious. Ikuko awakens and sees the sun dawning over the ocean, but she looks as though it causes inconvenience for her, hinting that Mother was able to take over her body before dying.
Mother is depicted as being a desperate figure, wishing to escape. Her attempts to manipulate people throughout the years as avatars show that she does not care for the feelings of others.
- Mate of Otoshigo
- Creator of Kanae; was angry at her for failing her mission
- Creator of Yuri Kishida avatar and fuses with her in Underworld in order to assume a body
- Manipulates Mamoru Itsuki into releasing her - fights him in her own dimension, and is defeated by him
- Hurt by Ikuko Kifune and fights her in Mother dimension - possesses her in the end
- Absorbs Shu Mikami
- Soji Abe sees her during release as Ryuko
- Mother is the first non-human main antagonist that is female.
- She is similar to Datatsushi in the sense that both bear some connection to mermaids, a half-woman half-fish creature of myth, as Datatsushi was called one in Hanuda's mythology. However, Mother resembles the traditional appearance of a mermaid - the top half of her body resembles a young woman's, while the bottom half is of a fish's. Datatsushi's larval form, on the other hand, looks vaguely fish-like and more insect-based.