18-Volt is a reoccurring character in the WarioWare series. He is a friend of 9-Volt and share the same interest in video games. His first appeared in WarioWare: Twisted! where he was a new student at Diamond Elementary. He wears a green suit and 3D glasses. He also carries a portable boombox.
18-Volt appears as a new student at Diamond Elementary where the teacher inquires what his hobby is, which 18-Volt responded to by playing music on his boom box. He gets in trouble, and after school, heads for his house angrily sulking. 9-Volt stops 18-Volt and informs him that he likes his music, the two become friends and 9-Volt invites him over his house. 18-Volt and 9-Volt end up playing video games on 9-Volt's Nintendo Entertainment System until 9-Volt's mother tells them to stop.
In WarioWare: Touched!, 18-Volt and 9-Volt get a copy of a new game, 36-Volt Man from the Toy Express. The two go back to 9-Volt's house and play the game late into the night.
When 18-Volt breaks 9-Volts Game & Watch in WarioWare: Smooth Moves, 9-Volt kicks 18-Volt out of his house. After being kicked out, 18-Volt goes to Toy Express to try to find a new Game & Watch for 9-Volt.
18-Volt is in the "Twist League". His microgames are "Nintendo Classics". In the story, he finds a sniveling kid and asks him. He points out that 13-Amp took his games. He was engaged in a rap battle. After he wins the rap battle, the kid thanked him for returning him his games. She praises him and told that she will beat him next time. Asking 18-Volt, she was shocked that 18-Volt is a " fourth-grader" who came from "Diamond City Elementary". 18-Volt tells her that she can meet her in the playground if she wants another rematch.