Remove the item from the belt and switch it back to gun mode and pull the trigger to activate the finisher. In addition, form change is possible by setting separately sold Ride Chemy Trading Cards. Lastly, using the Legend Kamen Riser on its own will activate a gunshot sound effect. When you set a Ride Chemy Trading Card and pull the trigger twice will activate a special finisher.
The DX Legend Kamen Riser cost 5,720 yen, and is set for an April 27th release. In addition, you can buy it as part of a set with the DX Legendriver for 11,770 yen.