Found wild in its forest habitat, Naetoru demonstrated strong protective instincts while caring for other Pokémon. This behavior led it to shield Satoshi's Pikachu from perceived threats, unaware of their connection. After Team Rocket's scheme involving Pikachu was thwarted, Satoshi successfully captured Naetoru as his first Sinnoh-region Pokémon. Naetoru initially displayed stubbornness, defying Satoshi's commands during a battle against rival Shinji shortly after capture, which resulted in defeat. Team Rocket later abducted Naetoru during another theft attempt, though Satoshi and companions secured its rescue. These events gradually deepened Naetoru's trust and loyalty towards Satoshi. Naetoru became vital to Satoshi's Sinnoh Gym challenge, playing a decisive role in the intense Oreburgh Gym battle against leader Hyouta. Facing Hyouta's fossil Pokémon Zugaidos and the formidable Rampardos, Naetoru endured punishing attacks yet secured victory. This critical win earned Satoshi the Coal Badge and triggered Naetoru's immediate evolution into Hayashigame.