"My name is Riolu. Riolu the Blue Cat"
Riolu is the blue cat who live in Snowdin with their best buddy Samael, and play a supporting role in the Neutral and True Pacifist Route and serves as the final boss and heroic antagonist in the Genocide Route.
After the Barrier
After the barrier has been shattered and the monster had went to the surface, an artist named Riolu wandered somewhere and a dog named, Toby Fox who send Riolu to Undertale world. Riolu shout “YOU!!!” and grab Toby, and then Riolu thought of something. He told Toby that why he was in this world. Toby told him that another artist named Samael who was in the world before Riolu came. By the few moment, Riolu asks Toby if he wanted to change the world as he wanted the changes a timeline to change the roles of every characters (including Riolu and Toby Fox). And thus, his wish is granted. The time is altered, memories of every people has been altered (except their personalities kept remains the same), until then, the backstory of the character has been altered. But however, Riolu was the one whose backstory had been completely rewritten as his memories of his past has been locked up by H. B. Mettaton (who is now take Gaster’s role) and altered his memories as Riolu’s story goes...
The rest of the story cannot be told yet.