Swelton is an obese Yo-Kai with two small horns on top of his head, and thick lips. He is always sweating, with the droplets oozing out of his body. He wears red trousers with black tiger stripes, and goes barefoot. He is seen with a white sweat towel on his right hand.
When first introduced in the anime, Swelton, in spite of his ability, feels a lot lonely for not making any friends because of said ability, suggesting that he can be open to new friendships when needed, as seen with Slicenrice. This need is further evidenced when, in later appearances, appears as part of the Heat clan.
Swelton has the ability of causing incessant sweating on the people he possesses. By rotating one of his horns, he can enable a mode in which said people can look handsome with the sweat droplets spreading out of their bodies; however, this has the drawback of causing said people to move at slow motion.
Swelton found the perfect friend into Slicenrice after the Samurai Yo-Kai noticed his sweating has the perfect salt quantity to make his rice balls delicious. Swelton, in turn, forged his first friendship thanks to said fact.
Swelton first appears in EP029, being the Yo-Kai responsible for Nate, Whisper and Jibanyan's incessant sweating. After revealing himself to them, Swelton tries to comfort them by enabling his "good-looking" mode; however this causes Nate and company to move at slow motion. Whisper informs Nate about Slicenrice, a Yo-kai known for slaying oni, and the kid resolves searching for him. Suddenly, Slicenrice himself appears and offers Nate and his friends, as well as Swelton, rice balls in order to commemorate their meeting, All of a sudden, Slicenrice realizes Swelton's sweating has enough salt to make his rice balls delicious; causing Swelton to broke into tears realizing he has found the perfect friend he has never met due to his incessant sweating. Their mutual happiness causes both Yo-kai to give their Yo-kai Medals to Nate. Later, Swelton and Slicenrice cook some rice balls, however Nate and his friends have their doubts into trying these rice balls due to how the salt for the rice balls was gathered.
In EP081, Swelton, along with Blazion, Sproink, and Swelterrier, hold a Heat clan party at the Adams Residence, causing Nate and his friends to feel extremely hot. The party is later crashed by Blizzaria's arrival, who forcefully pleads the four Yo-kai to eat cold food, causing them to freeze solid.
In EP091, Swelton and his fellow Heat Yo-kai compete in the White and Red Song Battle as the "Atti Soul Brothers" on behalf of the white team.