The Microbots are swarms of non-sentient, mind-controlled microbots whom originally Hiro Hamada's invention, but later turned into Yokai's robotic henchmen. They serve as the soulless secondary main antagonists of the 2014 Disney film "Big Hero 6".
The prototype version of these microbots (called Megabot) were seen when Hiro use 3 of them to participating in illegal robot fight. This robot later inspire him for making these microbots from there on with help of his friends and also Tadashi.
Stolen and Mass Produced
Hiro later bring them to the San Fransokyo Tech exhibition with the intention of using them to help improve society's efficiency. Unfortunately, the first generation of Microbots were stolen and used by Robert Callaghan to fake his death. Afterwards, he integrated the transmitter into a mask used for his identity as Yokai and began mass producing the Microbots to recollect the missing pieces of the Silent Sparrow portal. Once the portal was rebuilt, Yokai intended to use it to destroy Krei Tech as his revenge against Alistair Krei for causing the presumed death of his daughter Abigail. However, one Microbot that was kept by Hiro was reactivated due to Yokai's current use of the Microbots and tried to reunite with the rest. Hiro and Baymax then followed it and discover the Microbots' mass production by Yokai. Because of the duo's discovery of his plan, Yokai telephatically commands the Microbots to attack them, but the two are able to escape.
Despite the intrusion, Yokai continues to use the Microbots in his construction, excavating lost parts of the portal out at sea. While this is going on, Hiro and Baymax track him down again with the lone Microbot Hiro kept, which immediately joins with the other Microbots. However, Yokai spots them and their friends Honey Lemon, Go Go Tomago, Wasabi, and Fred, and goes on a rampage after them using the Microbots until the team is able to evade them.
Confronting Big Hero 6 on Alcatraz
When Yokai retreats to the island the portal was originally constructed on, the team (now upgraded into Big Hero 6) trace him there where Yokai attacks them. Knowing that the mask holds the transmitter, each member tries to remove the mask which would rob him of his control over the Microbots. Hiro manages to accidentally remove the villain's mask, temporarily deactivating the Microbots until Yokai escapes back with the mask.
The day after, Yokai intercepts Krei's latest ceremony and causes a swarm of Microbots to capture Krei and rise the rebuilt portal to destroy everything Krei has built. Big Hero 6 arrives on the scene, however Yokai uses the Microbots to incapacitate each member with the Microbot's overwhelming pressure bringing each near the verge of death. Fortunately, Hiro instructs his team to send the Microbots into the active portal in hopes of subduing Callaghan's power. The plan is successful, as each Microbot formation destroyed by a member causes a rapid decline in the Microbot numbers sucked into the portal until all of the Microbots disappear into the portal while Yokai's mask is destroyed by Hiro and Baymax.
Characteristics and Behind the scene
While teaser film and the earlier scripts for the Microbots shows that they originally possesses a degree of sentience, the final cut of the movie itself shows them as merely soulless minions for Yokai that more like puppets that he control for his nefarious purposes.
Interestingly, during the film's development, early incarnations of the microbots were more chaotic and organic with fluid like appearance (like either Symbiotes or pollymetic alloy that used for creating T-1000 from Terminator franchise), and instead acted as a special suit for Yokai. Eventually, the microbots would have lost the need for Yokai and try to assume their own identity. However, this idea was scrapped due to the demand for the Microbots' technology to be from existing science instead of comic science.