Like it says on the tin.
When Hiro goes into the portal, he finds himself somewhere else; a place full of hideously deformed human-like beings possessed of monstrous strength. And what comes out with him...is the strongest creature on earth: HANMA YUJIRO!
Well, since Baymax also makes it out, its up tho the kids and their robotic friend to stop The Ogre, before he makes the leaders of their world swear the Oath of Friendship and establishes himself as the first Brute Force Country in their world!
Can they beat Yujiro?
Or do they all die?