Not only was Spider-Man: Into the Spider-Verse one of the first big Marvel movies to feature a multiverse, it also did so with rave reviews and praise from fans. Featuring six Spideys from different timelines, some of the character's most obscure variations got their first appearance on the big screen. One such Spidey was the anime-inspired Peni Parker, who has a recent fan theory suggesting she made her way over from another Marvel animation: Big Hero 6.
Being one of the more recent additions to the Spider-Verse, Peni Parker was first introduced in the 2014 Edge of the Spider-Verse #5 comic. After the passing of her father, Peni was adopted by her Aunt May and Uncle Ben. She then began work on her father's Spider-Man mech-suit, powered by a radioactive spider who she let bite her. This suit, named the SP//dr, is the large robot seen with Peni during Into the Spider-Verse.
Other than being wrapped up in more Spider-Verse chaos, little else is known about Peni Parker outside of a few comics. However, a recent Reddit fan theory from user PrinceMarvelOz suggests that the Peni seen in the movie could very well have come from the same universe as Big Hero 6. While the theory itself doesn't offer any specific evidence, there's still some merit to the idea.
Big Hero 6 is another animated adaptation of a Marvel property, which brings the obscure group of heroes into the modern-day. Featuring a team of university geniuses, they each build their own suits and superpowers to help fight against the evil Callaghan, who seeks revenge for the disappearance of his daughter by opening up a portal into an unknown dimension. Although not as beloved as Into the Spider-Verse, there were still a lot of audiences who enjoyed Big Hero 6, including the highly-loveable inflatable Baymax robot.
When comparing Peni Parker to the world of Big Hero 6, there are plenty of similarities to be found. What makes the super-team stand out is the practicality of their creations, as their abilities all come from their scientific creations. The same goes for Peni, whose main power comes from her SP//dr suit. This technology would absolutely be feasible in Big Hero 6, as nanobots and AI play a big role throughout.
Also, the general aesthetic of Peni Parker fits in with Big Hero 6 rather well. While her 2D design in Into the Spider-Verse doesn't match the 3D models, her general look and personality could translate well into the movie. And with her frequent encounters with the multiverse, the reality-bending actions of Callaghan could factor into why they happen. The portal he opened doesn't look too different from the ones opened by Fisk in Into the Spider-Verse.
While there's little to back up this theory, most agree that Peni would make for a fitting Big Hero 6 version of Spidey. And with the upcoming sequel Spider-Man: Across the Spider-Verse, it seems the filmmakers are going even deeper into the multiverse and obscure Spidey-lore. So, being introduced to Peni Parker's world is within the realm of possibility.