San Fransokyo is a world in Kingdom Hearts III. It is based on Disney's 2014 film Big Hero 6. It is the most recent Disney animated feature to be incorporated as a world into the Kingdom Hearts series.
The layout of the city is a high-tech hybrid of artistic and technological architecture and a fusion of both San Francisco, California and Tokyo, Japan. Built on the coast of the Pacific Ocean (presumably in California), the city is designed to withstand the risk of further earthquakes. Animators added an extra spin to the Painted Lady houses of San Francisco by adding Japanese touches to them, such as the Japanese like roof tops, koinoibori flags, Japanese lanterns, signature cats etc.
San Fransokyo prides itself for its extensive focus on science and innovation. Esteemed universities such as the San Fransokyo Institute of Technology, are responsible for grooming some of the most significant figures in the scientific field, such as Alistair Krei. In fact, a large quantity of the buildings and technology in the city were constructed by Alistair and his company Krei Tech. Art has also been an important part of the city's culture as far back as the early 19th century, especially the work of Lenore Shimamoto.
Conversely, behind San Fransokyo's bright aesthetic is the underworld of illegal bot-fighting, mercenaries, and crime syndicates—commonly based in the dark, grungy alleys of the city.
Sora arrives in the metropolitan city of San Fransokyo and amid the chaos, he meets the members of Big Hero 6, Hiro and Baymax. With the appearance of the Heartless and a mysterious enemy gathering data, Sora, Donald and Goofy must adapt to the world around them and the Big Hero 6 team upgrade to fight the darkness.
After a first battle against the Heartless, the Big Hero 6 team gathers in Hiro's garage to meet his new friends and foes. Hiro gives Sora some AR glasses, to give him a new perspective on the city, collect new data and to train with the other heroes.
During training, Big Hero 6 observes Sora's fighting style and new ideas arise to combat the Heartless. In a new raid of darkness, everyone releases their new skills, celebrating their victory with an ice cream. Hiro tells Sora that the idea for Baymax and Big Hero 6 was because of his deceased brother Tadashi.
Back home, a mysterious enemy appears; dark cubes that wreak havoc on the city. All the members of Big Hero 6 are cornered and Hiro is alone in the garage, he begs Sora and his friends to free the others while he gathers more information about the Dark Cubes. Trapping the mass of Cuboscuros, a new member of the Real Organization XIII appears; Riku. But not the Riku that Sora knows, but a replica infused by darkness. This came to San Fransokyo by order of the Organization; create a heart from data. He then takes out a memory chip, the old combat chip that Hiro used for Baymax, and inserts it into the Dark Cubes, but it was not yet completed.
In the garage, Hiro explains that the old Baymax disappeared into a portal to another dimension, leaving him with Tadashi's memory chip to create a second Baymax. They all arrive at a new place, where Riku has the memory chip ready and with a new vessel; Dark Baymax. Hiro doesn't dare to harm Baymax because of the memory of his brother, so Sora confronts him with Baymax's help. Defeated, Hiro extracts the corrupted chip and makes the decision to destroy it himself. Later, the old Baymax awakens again to all of his friends, hugging Hiro and his twin Baymax.