DOKC Bio: Kase / Kamen Rider Siren

Name: Kase
Planet: Ryuki
Rider: Kamen Rider Siren
Weap / Vehicles: Advent Deck and Motorcycle
Bio: Kase is the sister of Len (Kamen Rider Wing Knight) and Slater (General Xaviax). Kase's home planet of Ryuki was invaded by the original Xaviax. Kase, Len and Slater defeated Xaviax but Xaviax's spirit took over Slater's body possessing him. Kase and Len were believed to have been dead but tracked Xaviax down once they learned he was conquering other planets.

Chap10: Kase was kidnapped by Xaviax's Minions was held prisioner and was about to be drained. Xaviax stole her Advent Deck so she couldn't transform and leave.

Chap24: Kase escaped from Xaviax's lair after battling him for the stolen Advent Deck and has returned to Len, Kit, and the Vented Drew again.

Chap26: Kase didn't believe Drew's change of heart and investigated. Kase found out that Drew rigged some testing to prove his honesty and eventually made Len Vent Drew once he tried to Vent them.