Zacian first appeared when Ash and Pikachu attempted to reunite with Goh after they got separated in the Slumbering Weald. The two came across the Warrior Pokémon as an illusion and attempted to battle it, though Pikachu's Iron Tail simply phased right through Zacian, surprising Ash. Zacian howled, creating more fog as it disappeared without a trace.
While finding statues that depicted Zacian alongside Zamazenta, Goh returned to the Slumbering Weald with Sonia to call for the Legendary Pokémon to help with the suddenly outbreak in rampaging Dynamax Pokémon. While wandering through the thick fog, Zacian and Zamazenta appeared before the two shortly before going back into the fog. Goh and Sonia followed the Legendary Pokémon only to find an altar with the Rusted Sword and Rusted Shield.
Ash and Goh headed to the Galar Power Plant to confront Eternatus, bearing the Rusted Sword and Rusted Shield. Suddenly, the objects began to glow as Zacian and Zamazenta retrieve them, causing them to transform into their Crowned Sword and Crowned Shield forms, respectively. Zacian uses Behemoth Blade and Zamazenta uses Behemoth Bash, helping Ash and Goh defeat Eternatus as Goh throws a Poké Ball at the once Eternamaxed Pokémon, successfully catching it. After the battle, Zacian and Zamazenta leave the scene, leaving behind their weapons.
Ash and Goh visit the altar where the weapons were as Zacian and Zamazenta approach them. Ash hopes to one day battle the strong Pokémon while Goh hopes to catch lots of Pokémon in the future.