Pokemon: A Passing Kamen Rider

There's a man who says he's a Trainer, looks like a Kamen Rider, and really is a Trainer.

Xiao Yi, the daughter of Ash and Serena, has a fateful encounter on her travels. She becomes the first Pokemon world's Kamen Rider, and will remain its only one. Yet she's still a Trainer, traveling across parallel universes to deal with Imagin who can transform into Pokemon.