Kero the Greninja

Kero is a Greninja from Lumiose City , Kalos with a cold-hearted and calm personality. He used to be a Froakie owned by an abusive female Trainer, but he escaped into the Moor of Icirrus when his Trainer went out for a coffee. He swam his way from Kalos to Unova using Surf. Yuuta found Kero after being rescued by Professor Juniper and he decided to take care of him. Eventually, Kero grew up and evolved into a Greninja after training with Yuuta and Miju. He became best friends with Miju and fought alongside him to protect the Unova region from threats. Thanks to his bond with Yuuta, Kero is able to transform into Ash-Greninja using his Battle Bond ability.

As Ash-Greninja, Kero is able to create a gigantic Water Shuriken that can cut through anything, including a Duraludon. However, if Kero takes damage, Yuuta will be hurt as well. Kero's sense of heroism is unrivalled, and will save anyone in danger with his ninja skills and Water-type moves. He hates bad guys, especially Inukai. However, Kero loves surfing, meditating and honing his ninjutsu skills.