Mochi originated from the film's storyboards by story artist Kendelle Hoyer who felt that Hiro and Tadashi's family needed a pet. Eventually, Mochi was finally moved into the film.
Mochi was originally going to have rocket boosters that were made by Hiro. Although Paul Briggs and screenwriter Robert L. Barid absolutely adored the idea, there was no way that it could be put into the movie in a way that would make sense in context with the movie. However, the idea was later recycled when Hiro and Tadashi were in San Fransokyo Tech in the background as someone's science experiment. When seeing some advertising for the movie in Japan and seeing the Japanese audience fall in love with the concept, Briggs said, "You guys do realize that Rocket Cat hasn't been in the movie for a year now?" as the idea was removed early on in production.
Mochi first appears in Lucky Cat Cafe after Aunt Cass returns from picking up her nephews Hiro and Tadashi Hamada. Cass, suffering from stress eating, calls to Mochi, who follows her into the kitchen.
After Hiro returns home from following the trails of his Microbots, Mochi appears, purring and rubbing against Hiro's leg when he tries to hide Baymax. After Hiro throws him up the stairs, it is quite possible that Baymax caught Mochi while calling him a "hairy baby." When Hiro arrives, Mochi dashes downstairs. When Baymax sneaks down again, Mochi and Aunt Cass are watching television. He is also shown in the end credits.
Mochi appears in the follow-up series as a recurring character. He is often seen around the Lucky Cat Café sleeping or being petted by Baymax. In "Mr. Sparkles Loses His Sparkle", Mochi becomes an online celebrity when Honey Lemon posts a video of him slow clapping. He becomes so popular that Mr. Sparkles, host of Maximum Insane obstacle Challenge, loses his fame. Consumed by jealousy, he kidnaps and threatens to send Mochi into space unless Go Go competes in a game. Even though beaten, Mr. Sparkles still launches Mochi in a rocket, but is rescued by Hiro's new robotic invention, Skymax.
- A painting of Mochi wearing a Stitch costume can be seen behind Hiro when he is talking to his aunt.
- Japanese bobtail cats (especially calicoes) are considered lucky blessings in Japanese culture, and Cass's shop, the Lucky Cat Cafe has beckoning cats as the main theme.
- Mochi's name comes from a type of Japanese rice cake, which is usually made in a special mochitsuki ceremony, and is usually served around the Japanese New Year.
- Mochi is a male cat, but has a calico fur pattern, which is found almost exclusively in female cats due to the calico gene being found on the X chromosome. However, male calico cats do exist, but are extremely rare (about 1 in 3000 cats is born a male calico).
- He can briefly be seen playing with a laser-pointer and sleeping on one of the microbot bins during Hiro's hard work montage.
- Baymax's infamous line while petting Mochi, "Hairy baby...hairy baby," became a popular Internet meme during the film's release.
- The bell on Mochi's collar is silver in the movie, but in the tv series, it is gold.