Prior to the start of the series, Sapphire received Rono as an Aron from her father, Professor Birch. He was present the day that Sapphire and Ruby were attacked by a Salamence, but was not used to help fend it off. Rono first appeared at the end of Distracting Dustox, as one of the four Pokémon Sapphire started her journey with.
In Lombre Larceny, Rono helped rescue Mr. Stone's Castform from a water fountain. With his ability to chew through metal, Rono was able to eat enough of the fountain for Sapphire to rip it off and rescue the Castform. It was soon revealed that Team Aqua was the reason Castform was trapped, and Rono and Chic were sent out to battle them. Both Rono and Chic defeated their Sharpedo and Carvanha, but took damage from their AbilityRough Skin. Due to the injury Rono was unable to take out Shelly's Ludicolo, but Chic was able to defeat it with help from Castform.
In Blowing Past Nosepass I, Rono was Sapphire's first choice against Roxanne and her Nosepass. After exchanging an attack Sapphire declares that Nosepass is too strong and decides to switch, but is unable to. Roxanne points out that Nosepass has Magnet Pull and switching Rono out is impossible. Nosepass then attacks with a barrage of Rock Throws and attempts to finish him with Rock Slide. Roxanne declares the match over, but Rono climbs out of the rubble and attacks. Due to Nosepass being unable to face a different direction than north, it loses its balance when it turns around, allowing Rono to beat it and give Sapphire the victory.
In Mashing Makuhita, Sapphire trains Rono and Chic at Granite Cave in order to prepare for her Gym battle against Brawly. After training for most of the day the two evolve into Lairon and Combusken. Sapphire then goes to Brawly and begins their battle. During the battle Rono is sent out against his Makuhita and immediately attacks with Metal Claw and Iron Tail. Using its Jū fighting style, Makuhita easily defeats Rono, and Sapphire recalls him just in time.
In Bubble Bubble Toil and Azumarill II, Rono battled Matt in a flooded cable car. Matt sends his Sharpedo in to finish Sapphire off and Rono jumps in the way and uses Iron Defense, breaking Sharpedo's teeth. While distracted Sapphire takes the teeth and pierces the glass, removing the water. With the water gone Rono smashes into them with Take Down and sends them flying.
Rono is a mischievous Pokémon and loves to play around, though he always listens to Sapphire. Like Sapphire, he has a love for battling and is very strong. He cares greatly for his Trainer. In battle, Rono is used for his defensive capabilities and tough exterior.