Riolu is the pre-evolutionary stage of Lucario. Despite being a small canine-like Pokémon, Riolu possesses incredible power. In this story, Riolu is rescued by Ember after a rift summons a monster. Thanks to Ember's transformation, she can understand other Pokémon, thus Riolu is given a voice to communicate to the audience. Much like Lucario, Riolu can sense the aura of other beings around him, albeit not as strongly. He also has a strong disdain for humans; he states that many Pokémon end up lost or trapped in the Castelia City sewers due to having no trainers. Thus, Riolu makes it his mission to help other Pokémon in need and despite knowing that Ember is human, he agrees to help her because she saved his life. 

Riolu's voice should be that of a young boy, sort of akin to something like Tails' voice from the Sonic the Hedgehog games.