Fullmetal Alchemist AU

Fullmetal Alchemist AU is an alternate universe in which the Big Four are portrayed as characters from Hiromu Arakawa's highly popular manga series, Fullmetal Alchemist.

About the AU
In Fullmetal Alchemist, Edward Elric and his younger brother Alphonse attempt to resurrect their dead mother using a forbidden Alchemal ritual. The ritual goes wrong, causing Edward's left leg and Alphonse's whole body to be 'taken' as a toll for trying to transmute a human. Ed than sacrifices his right arm in order to bind Al's soul to a suit of armor. With help from their close childhood friend Winry Rocbell and her Grandma, Pinako, the Elric brothers replace Ed's lost limbs with mechanical replacements, called 'auto-mail prosthetics. The Elric brothers than go on a quest to find the Philosophers Stone, a powerful Alchemal tool that they could use to return themselves to normal. To help with this, Ed becomes a state Alchemist, or a 'dog of the military' at the young age of 12, earning the title of Fullmetal Alchemist, and giving the brothers access to money and other reasources. The Big Four can be portrayed as either the main characters, taking the place of the Elric brothers and their friends, or as friends, allies, or even enemies to them.

Hiccup Horrendous Haddock III
Hiccup can be portrayed as Edward Elric, since they are both prodigies in their respective jobs, Alchemy and Dragon Riding/Taming, and both have an artificial left leg. However, Hiccups calmer and less overt personality is more akin to Alphonse, so Hiccup could also take his place. And Hiccups prowess with hand tools and the fact that he built his own leg is similar to Winry Rockbell and her skill with auto-mail limbs, and when Merida is portrayed as Ed, because of the Mericcup pairing. Another possible character for Hiccup to be portrayed as is Col. Roy Mustang, due to the shared affiliation with fire the two have. Hiccup can also be portrayed as an auto mail engineer that the Elrics and Winry meet in Rush Valley, or as another Alchemist prodigy. When Hiccup is portrayed as one of the Elric brothers, Jack is portrayed as the other brother, and vice-versa.

Jack Frost
Jack can also be portrayed as Ed, because they're both hot headed, wily, and older brothers. Because of Jacks invisibility in RotG, Jack can also be portrayed as Al. Jack sometimes portrays Winry, due to their similar personalities, and when Merida is portrayed as Ed because of the Jarida pairing. Jack can also be portrayed as Lin, because of there similar cocky personalities. Jack can also be a freelance Alchemist living up north near Briggs, specializing in Ice and Water related Alchemy. When Hiccup is portrayed as one of the Elric brothers, Jack is portrayed as the other brother, and vice-versa.

Merida DunBroch
Merida is most often portrayed as either Ed or Winry, due to the similar personalities and tempers, and the Mericcup and Jarida shippings. When Merida is in the role of Ed, Rapunzel usually takes the role of Al.

Rapunzel Corona
Due to her calmer and more optimistic disposition, Rapunzel is often portrayed as Al. Rapunzel can also be portrayed as Winry because the two both get excited when they get around something they're really interested in, (auto mail for Winry, and exploring the world for Rapunzel), and also because of the Jackunzel and Hiccunzel pairings. Rapunzel can also take the role of May Chang, since both are princesses, innocent, more capable in combat situations than they look, and associated with a known criminal. When Rapunzel is portrayed as Al, Merida usually portrays Ed.

Queen Elsa of Arendelle
The role Elsa plays in this AU is usually only one of two: Ed, or Al. Elsa is portrayed as Ed because both are the older sibling, and both feel responsible for a horrible accident that happened to their younger sibling. However, Elsa's calmer and more rational personality makes her more like Al, so she is also portrayed as him.

Princess Anna of Arendelle
Much like Elsa, Anna usually portrays one of the Elric brothers. She's portrayed as Al because she's the younger sibling, and as Ed because of her reckless attitude and her more hyperactive personality.

Kristoff Bjorgman
Kristoff usually only is part of the AU when Anna and Elsa are portraying the Elric brothers. He portrays Winry, because the two share a lot of similarities: both loose their parents at a young age, and are raised by someone they call a grandparent, both are experts in their chosen profession, which they've been doing since they were little, and both fall in love with someone who loves them in return, but doesn't realize or admit it until after they do.

Hiro Hamada
Despite his age Hiro is seen as Edward Elric or a alchemist that wanted to see his brother again, with Baymax (as a human) as a friend that wanted to help him do it. Hiro's robotic skills also cast him as a male Winry or a young auto mail engineer.

Tadashi Hamada
Tadashi is cast between (older) Alphonse and the desist; the reason why Hiro (as a alchemist) opened the door.

Baymax
Baymax's 2.0 armor acts as armor Alphonse Elric when his or Tadashis' soul is bind to it by Hiro (when he portrayed as Edward).