Kamen Rider Siren is one of the 13 Riders featured in the story, and the only female Kamen Rider. Kase is the original Kamen Rider Siren, with a swan Advent Deck, and is a fellow survivor of Ventara like Len. She is eager hunter who acts the complete opposite of Len, who was unaware that she had survived. During the time Adam betrayed the other Riders, she quickly took herself and Len out of suspended animation and managed to throw him into a mirror and is thought to have been lost by both Len and Xaviax. Before escaping, she managed to steal two Survive Mode cards for Dragon Knight and Wing Knight (unable to get her own in time). She battles Xaviax's monsters in secret and slowly makes her way back to Len.
Maya Young is a young woman who is investigating the mysterious disappearances and believes in conspiracies, getting caught up in the Kamen Rider battle. She is a member of the website WayAboveTopSecret.com, which is themed around conspiracy theories and strange anomalies, especially those centering around the Mirror Monsters. To this end, she enlists Kit's help in uncovering the mysteries surrounding Ventara and the Mirror Monsters, although Lacey thinks she's just trying to ask him out. Due to her attempted abduction by one of the Newt Monsters, she is able to see the Mirror Monsters when no one else can.
While discussing how to counter Xaviax's plans, Eubulon reassigns the Siren deck to Maya to help Len while he goes to retrieve the other Riders. He gives her the ability to fight by installing the memories of the previous Siren owner, Kase, making her the second Kamen Rider Siren. She later meets Chance, Price, and Hunt, some of the original Riders. Due to her past experiences with JTC, she feels uneasy around Price, despite his attempts to befriend her. During a confrontation against several Mirror Monsters, Maya meets up with Adam who attempts to befriend the Earth Rider since he failed with the Ventaran Riders. She is put off by his attempts, though not once did he attack her. Kit later shows up, and after arguing, Kit and Adam fight each other, though Maya wants them both to stop.
After Kase comes back from the Advent Void, Maya returns the Advent Deck back to her saying that fighting as a Kamen Rider was one of the best experiences in her life, but her journalistic career comes first.
She also manages to patch the bad relations with Price realizing that Price and JTC, though they look the same, are two different people.
Fighting Style
Though they share similarities in appearance and visor, Siren and Wing Knight have opposing combat styles. While Wing Knight specializes in chivalrous one-on -one combat, Siren leans more on multiple combat, using her Sword Vent to take down multiple enemies. She also has a set for on-on-one combat, using her Blanc Visor in conjuction with her Guard Vent. While Siren is more agile and forceful than Wing Knight, she is physically weaker, and she doesn't enjoy the use of Wing Knight's special vents (Trick Vent, Nasty Vent). But because Siren and Wing Knight have very similar styles, they work very well together. The Siren deck is the only deck that passes from two different people of two different DNA structures due to Eubulon's influence.
Visor and Advent Deck
Because of her appearance, Siren is often compared to Kamen Rider Knight as both have similar designs, contract monsters but in opposing color schemes and that Siren's cape is feathery. With her Blanc Visor rapier, she can conjure her Wing Slasher or execute her Final Vent Misty Slash.
- Advent (AP: 4000): Summons Blancwing, a white mechanical swan whose name is derived from the French word "blanc", meaning "white", being combined and "wing".
- Sword Vent (AP: 2000): Conjures Wing Slasher, a twin-bladed naginata.
- Guard Vent (AP: 2000): Conjures Wing Shield, modeled after Blancwing's wings.
- Final Vent (AP: 5000): Executes Misty Slash. Blancwing attacks the enemy from behind by producing a gust with it's wings sending them flying into the path of Siren's Wing Slasher.
