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 upset. 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.
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. 13-Amp asks the school which school he goes to: he answers that he goes to "Diamond City Elementary" which she was stunned, and mentions he is "in fourth grade", 13-Amp was even more shocked. 18-Volt tells her that she can meet her in the playground if she wants another rematch. She mentions to herself she was "bested by a fourth-grader".