It's been four years since Hiro had first met Baymax. At first, Hiro was unsure of his feelings towards him, finding him more of a nuisance than anything else. Over time, Hiro started to enjoy Baymax's company. He started feeling rather uncomfortable if he hadn't seen Baymax in a few days, and insisted on taking Baymax with him wherever he went. He refused to let anyone else be his doctor, as he was only comfortable with Baymax poking and prodding him.

Now, at age 18, he was very protective over Baymax. He wouldn't let anyone bring anything sharp near Baymax, even though he knew that Baymax could easily fix a puncture with tape. He'd always be holding onto one of Baymax's giant arms when they were walking together. He even developed a charging mat of sorts for his bed, so that Baymax could sleep next to him.

Baymax was also protective over Hiro. When he and the rest of the team went out to do superhero business, Baymax would always favor helping Hiro first over anyone else. After all, he was Hiro's healthcare bot. Not Honey Lemon's. Not Go Go's. Not Wasabi's, Fred's, or anyone else's healthcare bot. He would help everyone else, but Hiro was always first.

Go Go was the first to suggest that Hiro was dating Baymax, two years ago when Hiro was 16. Wasabi pointed out that it's likely that Hiro was dating Baymax since their first flight together. Hiro denied any claim that he was dating Baymax, but his friends knew better. They've seen how Hiro and Baymax are when they're together. Hiro sat on Baymax's lap while the group was together, and Fred had seen Hiro give Baymax kisses on multiple occasions. They didn't have an issue with his robosexuality; in fact, they were very supportive of Hiro. Hiro still felt very shy about his robot boyfriend and was in denial any time he was confronted about it.

Go Go sometimes catches Hiro remove a blue chip from Baymax's access port quickly and furtively before they go out on superhero business. She wasn't sure about its function, but she had a hunch. Hiro designed the blue chip two years back. Hiro's strong interest in robotics may have pushed him towards being more robosexual, but he sometimes watched human porn, and occasionally hentai. Hiro was somewhat kinky—he enjoyed some aspects of BDSM, and enjoyed macro/micro. He also watched a fair bit of gay porn, as being attracted towards a male-personified robot, made him in effect, partly gay. Despite all the porn Hiro watched, Hiro was attracted to Baymax, and only Baymax.

Similar to how he analyzed several karate videos for Baymax's red chip, Hiro analyzed several of his favorite pornos to program the blue chip. Hiro also added in many of his own programs—ones that were specific to Baymax and his functions—that Baymax could draw from to perform in a sexual act. Baymax's fourth slot remained unused so far, but when Hiro was alone, Baymax had this third chip installed into his system.