Her Gate target is Yoshikazu Kumagai, who is Haruto's elementary teacher. Siren can manipulates wind easily as her attacks. She also armed with a spear as her weapon.
She first appears on Donut Shop Hungry, overhears Kumagai and Haruto's chats about Kumagai wants a rare toy plane for his late son. When Koyomi arrives and detects the woman nearby Haruto and Kumagai is a Phantom. Siren then attacks them, but interrupted by Wizard. Though Wizard and Siren are equals, she decides to escapes. As Shizune, she hypnotized Wajima and he reveals to Shizune that he sold the toy plane to Tamotsu Sakai. When Haruto and Kumagai arrives at Sakai's house to get the toy plane, Siren had already obtained the toy. When she tries to destroy it, the toy plane was save by Griffon. Wizard and Beast then battle Siren and her Ghouls. Though Wizard then chases Cerberus PlaMonster, leaving Beast to finish the Ghouls all by himself. Though Siren escapes once again.
Later, Siren tells Syo Sakai, Tamotsu Sakai's son to steals the toy plane. After stealing the toy plane and will gives it to Siren, Haruto saves Syo and uses Bind Ring to prevents Siren to destroy the toy plane. When Haruto seeing Cerberus once again, he thinks to let Kumagai to fell into despair and let him to surpasses his Phantom. Though, if he can't he just rush to Kumagai's Underworld. When releasing Siren from chains, Shunpei holds Siren for some time until Beast appears and send Siren to retreats. The other then know that Syo wasn't hypnotizes, as he wants to destroy the toy plane since he wants to play with his father. Kumagai then destroys the toy plane. much to everyone's shocks. He says there is no point to having the toy, as his son already death and it broke Syo and his father's relationship. Though, Kumagai's son's smile always in his heart.
Later, Haruto and Kosuke meet Siren with the combination of all PlaMonsters. Wizard and Beast then fights Siren. As Beast Hyper, Beast defeats all the Ghouls. Though Siren overpowered Wizard Flame Dragon, she was overpowered by Wizard Infinity Style and soon destroyed by the Giga Dragon Shining.
- Gate: Shizune
- Episodes: 44-45
- Destroyed by: Kamen Rider Wizard Infinity Style's Giga Dragon Shining
- Mythological Basis: The Siren
- Height: 225 cm
- Weight: 154 kg
- Siren is based off an early Greek representation of her mythological namesake, in which the sirens are birds with large human female heads, bird feathers and scaly feet.
- Siren is the second female Phantom seen in the entirety of the series, after Medusa, as well as the deceased Inner Phantom, Jabberwock, who would have been female had Wizard failed in saving Rinko.
- Siren's costume is modified from Lizardman's costume.