The Jelsa Fandom exploded in November shortly after the release of Frozen. Along with an five-way crossover fandom known as The rise of the tangled frozen guardians,its part of a new and exciting online fandom of animated films.
Writers even portray that Jack may have saved her with his powers because she was a stillborn as a baby and he felt responsible and watched over her,Later falling in love with her.These two characters actually, although on the outside seemed to be very different they have a lot of common personality "wise" Their sacrifices and love for their younger siblings. (Jack died to save his younger sister;Elsa isolated herself to protect her sister whom she cared about even though it was killing her inside;sacrificing some of her childhood,all her teen years,the start of her adult life just to keep Anna and her family safe from her.) Their common change hair color,Jack was born with brown hair before becoming "Jack Frost" and Frozen confirmed that Elsa was really born with her powers,but if she was normal she would have had the same hair color as her mother,and their loneliness,Isolation (Jack was alone for hundreds of years and Elsa isolated in her bedroom,away from everyone.) and their also common in their powers to control ice and snow.They could bond and find comfort in each other. Jack didn't interact with someone for years and Elsa is locked in her bedroom for years.They could find comfort knowing that they are not alone, knowing that someone has also been going through as they were.
The two conflicting personalities is that Elsa is Quiet,regal,mature and reserved as a perfect queen for arendelle,while jack is loving,fun,mischievous,a trouble maker spirit,His prankster side could succeed in revealing the true personality of Elsa,Elsa is a cheerful and less serious,it seems (seen on the end of Frozen) They balance eachother out, Elsa showing the importance of being serious and Jack showing the importance of having fun and letting it go. This has become a quite popular ship.
Others would try to argue that Jack is over 300 years old and Elsa is 21 years old this a popular trope in fiction pairing an Immortal with a Mortal (Like an Immortal vampire and a Mortal girl) The tragedy of their seperation through the test of time a preferable tool for Drama and Tragedy.
Although nobody can touch you........ and nobody can see you.......... Remember... You will never be alone.