This takes place after the events of the Big Hero 6 movie and those of the story of  the video game; Persona 4 Arena Ultimax.

Atlus cheerily owns Persona. And Disney happily owns Big Hero 6.

Thanks to their inspiration, I'm just borrowing from them for this.

If you haven't watched the BH6 movie or played through (or watched video playthroughs) of Persona 3 Portable and/or FES, Persona 4 Arena (Mitsuru and Aigis stories), and P4AU, I suggest you do so! There are also four movies that adapt the P3 game.

But it's not necessary to be familiar with Persona to read this story. 

In fact, here's a recap of the events of the BH6 movie (big spoilers):

Hiro, a young teen, grows up from being a wayward bot fighter to become a brilliant inventor, reliable friend, and an unlikely hero.  When his brother, Tadashi, passes away due to circumstances caused by a trusted college professor,  Hiro must move on with his life.  His late brother's robotic invention, Baymax ends up helping him in this time.  Hiro tries to find out the truth of what happened, and Baymax, along with the late Tadashi's good friends (and students at the San Fransoko Institute of Technology) help him do so.

Wasabi is a physically powerful, obsessively tidy, organized guy.  He invented laser focused plasma; a powerful method of slicing through matter.  He gets flustered when things go awry, and had a tough time adjusting to life-or-death situations.  But he grew into a reliable hero that never hesitated to protect his friends.

Fred is a lanky comic book fan who hangs out at the SFIT lab with the others, but isn't a student. He's the school mascot! When the group needs a place to go after a crisis, he steps up to offer them sanctuary at his family's place.  He progresses from being merely silly to someone the others can count on in a crisis.  Still with his humor though!

Honey Lemon!  A tall, cheerful, compassionate, fashionable, specialist in chemistry.  She's very observant of people and situations.  Honey stands up for what she feels is right.  She's a bit nervous and has a rough start at becoming a heroine, but quickly becomes a valuable member to the team.

Go Go is a cool young woman of few words and a bit of an attitude who has invented MagLev discs as wheels for high-speed cycling.  She can be sarcastic to the others and a bit abrasive at first.  But after her experiences with the others, she works hard to protect them.  Even emotionally, as she becomes a big-sister figure to Hiro.

Baymax is the personable, highly advanced health care robot created by Tadashi.  He changes immensely from being a blank slate sort of a character to one who keeps learning: how to fight, protect, human expressions, emotions, and much more!

The reason I felt compelled to write this crossover was due to the similarities of Hiro and Mitsuru.  Many readers won't be familiar with Persona, but it features a highly developed cast of heroic characters with strong motivations.  Mitsuru experiences the death of a loved one due to betrayal, as does Hiro.  Both have a robot companion that grows considerably and is a close friend.  And Japanese culture is an aspect of both franchises.

Enjoy the story!