Gunbain first appeared in PASS12, where he was seen chasing Sonia in a fit of rage. Henry tried to stop him with Lancelot, but the moment he tried to attack Lancelot turned around and attacked Henry. Raihan tried to help only to be stopped by Henry, who figured out that Oranguru could control others with his fan. They quickly figured out Oranguru could only control one Pokémon at a time and sent both their teams at him. This overwhelmed Oranguru, as he struggled to control the Pokémon he wanted to. Learning that Sonia accidentally damaged the fan, Henry has everyone hold Oranguru down long enough for him to fix it. Now better, Oranguru calmed down and, as a show of thanks, asked to join Henry's team. Henry accepted and gave him the name Gunbain.
In PASS13, Gunbain was Henry's second choice in his gym battle against Allister, going up against his Cursola. Due to Cursola's ability to paralyze anything that touched it, Gunbain struggled to keep himself out of harm's way. They managed to overcome the issue by focusing on the physical body at the bottom and using Foul Play, which defeated the Coral Pokémon. Allister next sent out Gengar. It immediately Gigantamaxd and used G-Max Terror, trapping Gunbain and preventing him from switching out. Henry, however, countered by Dynamaxing Gunbain. The Sage Pokémon barely managed to avoid a Max Ooze from Gengar, then used Max Guard to protect himself from the next one. With Gengar's Gigantamax used up, Gunbain finished the battle with a Max Darkness.