Ash Ketchem: Well my story is a pretty screwed up one.
Ash is walking down the streets of Vale when he sees a group of criminals enter a store.
Ash: I'm actually not from this universe actually.
Ruby Rose crashes through the store window as the criminals step out of the store to confront her, only for her to pull out a giant scythe, making Ash look in confusion.
Ash: I originally wanted to be the very best, but me and one of my closest partners.
Ash and his most powerful water-type Greninja fall through a wormhole while battling Team Rocket.
Ash: And we apparently fused together.
Ash, who had since gained the attention of the criminals stepped infront of Ruby before a veil of water formed around him.
Ash: From the looks of things, I became someone else, something else.
The water vortex then vanished revealing Ash in a new form one that happened to come along when he and Greninja fell through the wormhole. Ash-Greninja!
Ash: I became Ash-Greninja.
After he finished talking he turned to see the four girls, Ruby, her sister Yang Xiao-Long, Weiss Schnee, and Blake Belladona.
Ash: So, any questions?
Yang was the only one to raise her hand, making Ash look as he found her the most amusing.
Ash: Yes, Yang.
Yang Xiao-Long: How can you kill an Ursa with just a water star?
Ash-Greninja jumped through the air as he threw two water shurikens, striking down two Ursas right infront of Team RWBY, and Team JNPR.
Ash: Skills I guess.
Ash-Greninja of Remnant
Ruby Rose: How fast can your form make cookies.
Ash facepalms.