As a wild Pokémon
Meltan first appeared in SM111, where it and several other Meltan arrived on Melemele Island. While investigating the sewers, the Meltan were divided into two groups and one ended up at the Ultra Guardians base under the Pokémon School. After being chased out by Lusamine's Clefable, they encountered Ash and his classmates, who decided to study the newly discovered species. During their study, the Meltan scattered, save for a lone Meltan that decided to take a nap next to Ash's Rowlet. When Rowlet accidentally startled Meltan and caused its hex nut to fall off, Rowlet retrieved the nut before a wild Murkrow could steal it. Taking a liking to Rowlet, Meltan chose to sneak inside of Ash's backpack, causing Ash to unknowingly take it home with him.
In the next episode, another incident with a Murkrow caused Meltan's hex nut to land in Team Rocket's van. After a failed attempt to replace the nut, Meltan and Rowlet encountered Team Rocket, who tried to capture them. When Meowth attacked, Rowlet defended Meltan by taking all of Meowth's attacks, leaving it unable to fight back. Rowlet's pain angered Meltan, who proceeded to defeat Team Rocket with a powerful Flash Cannon. Afterward, Ash arrived and brought Rowlet and Meltan back to the Pokémon School. Seeing how it bonded with Rowlet, Ash offered Meltan to join his team, which it accepted after saying goodbye to its Meltan friends.
With Ash
In SM117, Meltan rode Sandy's back for the duration of the group's visit to Malie City. When Mallow's hair ornament was blown away by the wind, Shaymin chased after it, and Sandy and Meltan followed Shaymin. After Sandy and Meltan helped Shaymin recover the hair ornament, the three Pokémon were imprisoned by Team Rocket. However, Meltan was able to eat a hole into the cage, allowing the three Pokémon to escape. Team Rocket then sent out their Pokémon, resulting in Sandy getting poisoned by Mareanie's Sludge Bomb and Mimikyu easily dodging Meltan's Flash Cannons. However, Ash, Mallow, and Lana showed up. Ash had Meltan attack Mareanie, whose Sludge Bomb was ineffective against it, allowing it to land a Headbutt on the Brutal Star Pokémon before Sandy finished it off with Double-Edge.
In SM118, while Ash was battling against Ryuki at the Kantonian Gym, and Rowlet was losing to Ryuki's Zweilous, Meltan angrily retaliated by eating away some of the decorations on Ryuki's suit. Ryuki then changed the battle into a Double Battle, with Ash using Rowlet and Meltan against Ryuki's Zweilous and Druddigon. Due to its slow movements, Meltan was unable to dodge Druddigon's Dragon Claws and was forced to try to protect itself with Harden. As Meltan's endurance was running low, Rowlet's Peck suddenly evolved into Brave Bird, allowing it to save Meltan from being defeated. Rowlet and Meltan then launched a combination attack at Zweilous and Druddigon, defeating them and winning the battle for Ash.
Meltan is a naturally curious individual who is prone to wander off on its own. It formed a very close friendship with Ash's Rowlet after it protected it from Meowth's Fury Swipes. Also, Meltan looks up to Rowlet and sees it as a mentor figure, much like Ash's Noivern's relationship with Hawlucha. Meltan gets easily scared, as seen in SM111, where it was reluctant to follow its fellow Meltan into the sewer, only following when it was forced. Despite being scared, Meltan will help its friends in any way it can. After joining Ash's team, Meltan easily became close to Ash and became friends with its teammates. Meltan also becomes very upset whenever it loses its hex nut.
Like many of its species, Meltan consumes anything made of metal, as seen in SM112, when Professor Burnet discovered a frying pan partially eaten. Frying pans in particular appear to be Meltan's favorite food. In the Poké Problem segment for SM115, Meltan was seen happily consuming the frying pan Ash and Pikachu were using for target practice. In SM116, Rowlet had to stop it from eating another one of Burnet's pans. Rotom later mused that it had already ruined three pans. This tendency came in handy in SM117, when it, Sandy, and Shaymin found themselves stuck in a cage made by Team Rocket. This was shown again in SM120, when it ate the metal on a hunter's ship to help free a Kyogre. Because of its liquid body, Meltan cannot move very fast, and is often seen chasing after friends or other things that draw its curiosity or riding on Rowlet. Meltan's slow movement prevents it from dodging well, causing it to rely on moves like Harden to endure enemy attacks.
Inside and outside of battle, Meltan has a tendency to act on its own without any input from its Trainer. This was showcased in SM118, where it attacked Ryuki because Rowlet was losing to his Zweilous. Later, while battling Ryuki's Druddigon, Meltan followed up an unsuccessful Headbutt with an unprompted Flash Cannon, surprising Ash.
