Reshiram first appeared in A Relic From the Past!, where it was seen in Relic Castle, sealed inside the Light Stone. N recovered the stone and took it to Dragonspiral Tower.
In Awaken the Legend!, N succeeded in releasing Reshiram from the Light Stone and proceeded to catch it. He then sent it out to battle Lewis, where it defeated the entirety of his team with ease.
It reappeared in Storming the Castle!, where it seen with N in his throne room. Reshiram witnessed Lewis release Zekrom from the Dark Stone and prepared to battle it.
In A Clash of Truth and Ideals!, Reshiram battled Zekrom in the skies above N's Castle. The vicious battle nearly ended in Reshiram's victory, but Lewis was able to encourage Zekrom to keep fighting. Reshiram was eventually defeated by a powerful Fusion Bolt.
After the battle, Reshiram left with N and Zekrom so that N could learn more about being a Trainer.
Reshiram returned with N and Zekrom in Fusion for the Future!, where it used Fusion Flare to save Lewis from being frozen by Kyurem's Glaciate. Alongside Zekrom, Reshiram began to battle Kyurem, but was forced back into the Light Stone by Kyurem's Absofusion, giving it the ability to transform into White Kyurem. After Reshiram was reminded of its bond with N, it separated from Kyurem and teamed up with Zekrom to take it down. The two managed to defeat Kyurem with a combination of Fusion Flare and Fusion Bolt. After Ghetsis was arrested and Kyurem retreated further into Giant Chasm, Reshiram left once again with N and Zekrom.
Reshiram was shown to have a very strong connection with N, as it sensed his strong desire to know the truth about whether humans and Pokémon could be friends. Reshiram follows N's commands in battle without question, showing its faith in the Hero of Truth.