The bot was made by Hiro, who used it against Mr. Yama and won, intending to continue using it in more bot fights until he decided to leave this career behind.
Though it appears to be a relatively simple model, Megabot's appearance is meant to be deceptive - its body is comprised of magnetic joints, which allows it to split into smaller parts of itself and attach to opponents, taking them apart and utterly defeating them with their own weapons. When switching between normal mode and battle mode, the robot's face switches from a yellow smiling face to a red, fierce-looking face.
Hiro watched Yama fight another bot fighter using his Little Yama bot. After Yama destroyed the fighter's bot, Hiro stepped in with a scared look, challenging Yama with Megabot. Everyone in the place laughed at its design and Yama accepted, believing it to be easy money. Megabot then was "destroyed" by Little Yama.
Hiro asked for a rematch, but Yama told him to accept defeat. Hiro then offered more money and Yama agreed once more. This time, Megabot switched to his "battle face" and Hiro, who was just pretending to be inexperienced, quickly destroyed Little Yama. After winning, everyone was shocked and Hiro took the money. Yama realized he was tricked and tried to attack Hiro, who was saved by his brother Tadashi in his scooter. The brothers escaped and Megabot stayed behind with Yama, but started attacking him and caught up with Hiro and Tadashi while they were followed by Yama's Thugs.
The police also arrived, followed the bot fighters and apprehended them. Tadashi was incarcerated with them for a short time until Aunt Cass arrived and took both of her nephews back to Lucky Cat Café. Despite what had just happened, Hiro already planned to attend another fight with Megabot that same night. Tadashi then took his brother to the San Fransokyo Institute of Technology trying to change his mind about his future. There, both met Robert Callaghan. Callaghan looked at Megabot and said that his own daughter also used to be into bot fighting when she was younger.
Hiro left with a great impression about the SFIT and decided to leave bot fighting in favor of joining the school. He tried to think of an outstanding invention to showcase at the SFIT and be accepted, but had no ideas at all. Tadashi then told him to look for another angle, and so Hiro stared at his Megabot's design, which inspired him to build a new invention: Microbots.
Later, after Tadashi's unfortunate death, Megabot inadvertently helped to activate Baymax when one of its legs fell onto Hiro's foot and reacted from the pain.
The Megabot then simply remained inside Hiro's room with no plans of being used by him anymore as he was no longer interested in bot fights.
In the series' episode "Food Fight", Megabot is spotted by Aunt Cass in Hiro's room. Since Hiro was now part of a superhero team, he had to go out a lot to help people but never told his aunt, as he didn't want to worry her. Cass went to his room and Hiro was absent (the team was helping Alistair Krei at that moment). She called Hiro, who lied saying he was studying, then Cass saw Megabot and believed Hiro had gone back into bot fighting, and so she went out at night to find him.
- Megabot's name is a pun on the word "mega", which means huge, in contrast to Megabot's small figure.
- Megabot has three additional faces in the Big Hero 6: Bot Fight app game: silly (blue), laughing (green), and angry (purple). Each one matches the five elements, including its happy and battle face.