Megabot was built by Hiro to be used in underground bot fights in San Fransokyo. Although it appears to be an inferior model compared to most bot fighters, its design is meant to be deceptive; it can split into smaller parts of itself and attach to opponents, taking them apart and utterly defeating them with their own weapons. Hiro used it against Mr. Yama and won, and intended to continue using it in more bot fights until he decided to leave this career behind. Afterwards, Megabot's layout and design is used by Hiro to build a new invention, Microbots.
When Tadashi died, Hiro went back to Bot Fighting with Megabot by his side, without Cass Hamada knowing. One of Megabot's legs falling on Hiro's feet and making him say "ow"; got the young Hamada to activate Baymax. Hiro was fixing his robot's leg, before he realized that Baymax had walked out of the house and went after him.