As the two are from different series, they have never met in canon. Even though they are both the main protagonists of DreamWorks film, who have originate from older source material than their respective fantasy-advance films.
Both Hiccup and Jack have naturally brown hair (although Jack's hair has been white since he became a Guardian), have flown through the air, with a little from Toothless and the wind, carry their iconic weapons with them, Jack's crock staff and Hiccup's flaming sword from How to Train Your Dragon 2. In Race to the Edge an earlier version of Hiccup's sword it damaged in an icy cave, but had manged to repair and make it better before the events of the second film. Similar to how Jack's staff was snapped in half when he was in a snowy area before they were both tossed into a deep chasm, but after Jack realized that he isn't beaten yet he repairs his staff. Their iconic weapons also given them power over an element that is commonly by their side, fire and ice. Just as Toothless and Baby Tooth have stood by Hiccup and Jack throughout their journeys, and were there to witness Hiccup becoming Berk's new chief while Jack becomes the fifth Guardian of Childhood. Hiccup is also part of a group that protects others from harm.
For a long time both Jack and Hiccup had left invisible, even though in Jack's case he really was invisible to the children that don't believe in him, despite all the effort he puts in the winter fun he makes form. While Hiccup had left like an outcast within his own tribe from not being Viking material, until he tamed a dragon and brought peace to both humans and dragons. Just as Jack restoring Jamie's faith in the Easter Bunny had finally gained him his first believer, before they work together to gather a few others in order to help the other Guardians. Hiccup has also been shown to be kind towards both human and dragon children, before he became the father of his own children. In a deleted scene from Hiccup's third film, his child self had chose to help an injured bird, which is a bit similar to how Jack had saved and cares for his bird-like fairy friend Baby Tooth. The two have even found themselves in the lairs of their main antagonists, without realizing that they were being brought to them until it was too late, while they were with Astrid, Toothless and Baby Tooth. With help from their friends, Hiccup and Jack were able to defeat the Red Death and Pitch, along with freeing many dragons and Toothiana's captured fairies from them.
Hijack is part of the Rise of the Brave Tangled Dragons crossover, where the two are part of the Big 4 along with Rapunzel from Tangled and Merida from Brave, and the only slash ship of the Big 4. They are also part of the smaller, How to Train Your Guardian crossover. It is the most popular slash ship for both characters. On AO3, it is the most written ship for Jack and the second for Hiccup, behind Hiccstrid.
As Jack Frost originates from Nordic myths and Hiccup is a Viking, it is possible for Hiccup to believe in Jack. In addition, the large amount of snow in Berk could be due to Jack visiting the island frequently. This could lead to Hiccup meeting Jack, as Jack is a spirit and can only be seen by those who believe in him. Because Jack an immortal while Hiccup is a mortal, however, it got fans to argue over the said fact. It has also presented a popular trope in fiction pairings of an immortal with a mortal (as an immortal vampire with a simple mortal human), the tragedy of their separation through the test of time a prefereabl tool for drama and tragedy.
As a main Big 4 pairing, it is common in many AU scenarios. When cast in roles, Hiccup is typically cast in the role of a female character, although this can vary depending on the AU and fan. One example is the Miraculous Ladybug AU, where Hiccup is cast as a male Ladybug and Jack is cast as Cat Noir. In a WALL-E AU, Hiccup takes the role of WALL-E and Jack takes the role of EVE. There have also been Monster/Vampire AU's that Hiccup as a vampire hunter who falls for a vampire (Jack) that he wouldn't bring himself to kill. This idea is due to them being featured as an immortal-mortal couple, along with Hiccup seeing the good in those who other have deemed as monsters and fans believe that it would help Jack to draw closer to Hiccup.
There have also been times when the ship has Jack as the Light Fury's rider or human trusting friend. Since both Hiccup and Toothless have green eyes, while Jack and the unnamed Light Fury's eyes are blue. Along with ROTBTD/ROTBTFMD fans creating fanon netizen versions of Jack and Hiccup from a DreamWorks website that resides within the digital, internet city world/universe from Disney's Ralph Breaks the Internet, whenever they feature either one of them with the netizen versions of Merida, Rapunzel, Elsa, Anna or Moana from Oh My Disney, since fans sometimes have the five female Disney characters in the modern style clothes for a Modern AU. While Hijack can simply have the two DreamWorks characters as friends of five Disney, netizen characters, so they can feature the romantic or friendship side of the DreamWorks crossover ship in a Wreck-It Ralph/Ralph Breaks the Internet AU.
- Hijack tag on DeviantArt
- Frostcup tag on DeviantArt
- Hiccup-x-Jack fanclub on DeviantArt
- Jack-Frost-x-Hiccup fanclub on DeviantArt
- Xx-Jack-x-Hiccup-xX fanclub on DeviantArt
- Hijack posts on Tumblr
- Frostcup posts on Tumblr
- Hijackelsa refers to the ship between Hiccup, Jack and Elsa
- Hijackless refers to the ship between Hiccup, Jack and Toothless
|SHIPS||het||Astret • Dagala • Heatcup • Heathlegs • Hiccanna • Hiccelsa • Hicclena • Hiccpunzel • Hiccstrid • Mericcup • Moaccup • NightLight • Stalka|
|femslash||Astriana • Astrunzel • Heastrid • Heathelsa • Meristrid • Valkinor • Valkstrid|
|slash||Dagcup • Eretcup • Hijack • Variccup|
|family||Dagther • Stoccup • Valccup|
|friend||Dagurmaster • Toothcup|
|CHARACTERS||male||Dagur the Deranged • Hiccup Horrendous Haddock III|
|female||Astrid Hofferson • Heather|