In Kiva...the last Rider Season...Wataru can only destroy the bodies of the Fangires while their soul is able to roam to either merge with other Fangire Energies to form a Sabbat (a fangire giant) or regenerate a new body, so Castle Doran has to eat the Fangire Life Energy to imprison them.
The only Riders that could completely destroy a Fangire (soul and all) are the Gold IXA (aka 2008 IXA or IXA Ver. X)/Keisuke Nago, Kamen Rider Saga, Dark Kiva...Wataru would later be able to destroy Fangires completely when he gained Emperor Form and the Zanvat Sword before hand Wataru in Kiva Form, as well as his other Forms and Dogabaki (his combo form) could only destroy the Fangire Bodies. In the past, the Prototype Bronze IXA could only destroy the bodies, but not the souls.