Another theme is growth. They could start off as just acquaintances and then develop into closer friends or more. Maybe one of them has a personal flaw that the other helps them overcome, which is a great way to show character development in the context of their relationship.
I'm not sure exactly which specific fanfictions would be the best, but you could also try checking out some Tumblr blogs dedicated to the fandom. Sometimes fans share their own fanfiction or recommend their favorites there. They might have some really creative takes on female Jack and Bunny, like putting them in alternate universes or giving them new powers and seeing how that affects their relationship.
One major theme is the idea of acceptance. They come from different backgrounds (in the context of their original stories), and the fanfiction often shows how they accept each other's quirks and differences. Also, adventure themes are common, as they go on various quests or face challenges together, which strengthens their bond.
A common theme is the exploration of their different natures. Bunny is often associated with spring and growth, while Jack Frost is all about winter and cold. Their coming together and finding harmony despite these differences is often explored.
Perhaps in the fanfic, the Easter Bunny gets lost in Jack Frost's frozen world. Jack Frost initially teases the Bunny but then realizes the Bunny is in danger. He helps the Bunny find his way back home. Along the way, they learn about each other's powers and cultures. The Bunny shows Jack Frost the beauty of new life that comes with Easter, and Jack Frost shows the Bunny the wonder of his ice sculptures.
One common theme could be unrequited love. Maybe Jack Frost has feelings for Bunny but Bunny doesn't feel the same way, or vice versa, which leads to a sad situation.
One great 'jack x bunny fanfiction' is 'The Unlikely Bond'. It beautifully weaves the relationship between Jack and Bunny, exploring their adventures in a new and exciting way. The characters are well - portrayed, staying true to their original personalities from the source material while also showing growth in their relationship.
A lemon fanfiction involving Jack Frost and the Easter Bunny might be about their unexpected encounter. Maybe they start off as rivals, each with their own season - winter and spring. But as they interact more, they discover a strange connection and start to see each other in a new light. However, this is just a basic idea as lemon fanfictions often involve some level of romantic or sensual undertones which can be developed in various ways.
One common theme is the clash of their different natures. Jack Frost represents winter and cold, while the Easter Bunny is all about spring and new life. Their differences can lead to interesting conflicts at first.