Baymax was designed to be a healthcare robot by Tadashi Hamada. After Tadashi's untimely death, his younger brother Hiro Hamada formed an attachment to Baymax, who diagnosed the boy with depression and hopes he could help him overcome it.
After Baymax found one of Hiro's microbots he built for the day Tadashi died, he followed the microbot with Hiro in tow, only to stumble across a supervillain who stole Hiro's technology. After another encounter with the villain Yokai, where the two of them were saved by Tadashi's old friends, Hiro decides that the town needs heroes and upgrades Baymax into a crime-fighting robot, forming the Big Hero 6 with their friends; Wasabi, Honey Lemon, Go Go Tomago and Fred.
