"Big Hero 6" broke an incredible record as the film brought in more than $621 million worldwide, making it the number one animated movie of 2014. Aside from making a killing at the box office, the film also won an Oscar for Best Animated Film, and with all of the movie's success, it's no wonder that a sequel is about to follow soon. 

Iconic comic book creator Stan Lee himself confirmed the news when he spoke to Toronto Sun back in April about Marvel's upcoming slate of movies. 

"After Ant-Man, we're going to start playing around with Doctor Strange, the Black Panther, the Inhumans, and then we have to come back for Guardians of the Galaxy 2, Big Hero 6, the Avengers, Captain America," said Lee. 

Since Lee's interview, very little has been said about the "Big Hero 6" sequel, but rumors about the film's plot have started circulating online. One persistent rumor making the rounds is about Tadashi being alive. According to Jon Negroni of Movie Pilot, the character will be the main villain in the upcoming film. 

In "Big Hero 6," protagonist Hiro Hamada wants to get accepted into a robotics program at the university where his brother, Tadashi, and his friends attend. When a fire breaks out at the university, Tadashi rushes in to rescue Professor Callahan, the head of the university's robotics program, but the building explodes moments later. Callahan survives, but Tadashi doesn't make it. 

However, Negroni speculates that Tadashi is alive and well.

"Look, if you know anything about movies, it's that if there's no body, that character is alive," he said. 

Negroni said that Tadashi rushing into the building, only for it to explode, is a purposeful setup for the character to become Sunfire, who is one of the original members of Big Hero 6 in the comics and is a prominent character in the Marvel Universe. In the comics, Sunfire reluctantly joins Big Hero 6, but gets possessed by an enemy and becomes a villain. 

So far, there has been no confirmation about this theory, but if the "Big Hero 6" sequel is staying true to the comics, then there is a very strong possibility that Tadashi could return for "Big Hero 7."