Upon hatching, Riolu was shown to be looking for a fight by using Vacuum Wave on anyone it sees. It even has a proud personality, and can be cocky and reckless, such as trying to fight against other wild Pokemon that was obviously stronger than it. At first, it wasn't the most open type as it refused to hatch without finding a trainer with a matching aura and was distrustful towards Ash but gradually warmed up after meeting Ash.
As an egg
Riolu was originally an egg from Sinnoh that got imported to Kanto. It was passed down from one Trainer to another, but it refused to hatch as it found these Trainers unmatched for it. It then sensed Ash's aura being transmitted to it during Ash's battle with Hashiba. Finding Ash worthy, Riolu finally hatched after Nurse Joy handed it to Ash.
As a Riolu
Upon hatching, Riolu was greeted by Ash, Pikachu, Go and Raboot. But out of distrust, it then shot a Vacuum Wave at Ash, jumped out of the window and runs away from the Institute. As Riolu left the Institute, it encountered a lot of wild Poliwarth, Poliwirl, and Poliwag, Butterfree, as well as some Ratatta and Diglett, but got attacked by them. When Riolu encountered an Onix, Ash and Pikachu arrived and protected Riolu from it. Then Riolu sensed the aura within Ash who battled Onix with his Pikachu. After realizing Ash was the one who possesses the powerful Aura, Riolu pushed Pikachu aside and decides to battle with Ash. Thanks to Ash's commands Riolu was able to defeat Onix. At the Pokémon center, Riolu had its wounds healed and decided to come with Ash, which Ash accepted, thus joining his team.
- Riolu is Ash's first Baby Pokémon.
- Riolu is the first Pokémon Ash hatched from an egg since his Noivern as a Noibat.
- Riolu share similar traits with Ash's Scraggy:
- They both are Fighting-type Pokémon
- The both given to Ash as a Egg and then hatch.
- Riolu's Pokémon Egg is a reference to the 10km Egg in Pokémon GO
- In many ways, Riolu capture make up the the other Riolu in Diamond and Pearl series where met it and form a close bond with but never officially caught it.
At Oak's Lab
At Kukui's house
At Cerise Laboratory