Here's my offering to this magnificent occasion:

Magischer Kriegers by RedRat8 - Magical Girl Lyrical Nanoha/Kamen Rider
The Stu in question is the offspring of the titular rider of Kamen Rider Wizard, Horuma and another rider by the name of Mayu (one of the few female riders that never died). The Stu also appears to be shoehorning Kamen Rider into the TOS, which would probably temporally displace any members of the canon. Not to worry though, me and Des got this one covered.

~Mattman The Comet, who almost didn't close the bold there