In such fanfiction, Kirby is often depicted as his cute, round self, but with a more tender side when it comes to his feelings for Jigglypuff. He might use his unique abilities to protect or impress Jigglypuff.
One possible storyline could be that Kirby and Jigglypuff are in a magical forest. They start as rivals, competing for the same delicious fruit. But as they interact more, they gradually develop feelings for each other. Their kiss could be a moment of realization of their new - found love, perhaps with a soft, warm glow surrounding them.
Kirby is known for being cute and friendly. His friendly nature might make the kiss a very innocent and warm moment. He would approach the kiss with his usual openness. Jigglypuff, being a bit more of a diva with its singing, might make the kiss more dramatic, like it's the grand finale of a performance.
Another theme is competition in a friendly way. They might compete in things like a singing contest (even though Kirby doesn't really sing in the original game but it can be a fun concept in fanfiction) or a race, and through this competition, they learn more about each other and grow their friendship.
Imagine Kirby bouncing around in a meadow and suddenly hears Jigglypuff's song. Kirby has never heard such a lovely sound before. He approaches Jigglypuff, and Jigglypuff stops singing for a moment, a bit startled. But Kirby's big, innocent eyes make Jigglypuff relax. They start to interact. Kirby shows Jigglypuff his amazing ability to inhale enemies, and Jigglypuff shows Kirby how it can inflate itself. As time passes, they develop feelings for each other. Their love story is like a fairytale in the world of cute characters, full of discovery, friendship, and eventually, love.
I'm not sure of specific fanfictions about Kirby and Jigglypuff in love. You can try searching on popular fanfiction websites like Archive of Our Own. There are often many creative works there.
One idea could be a story where Jigglypuff and Kirby team up to save their shared world from an evil force. Maybe there's a dark wizard who is stealing all the food in their land, and Kirby's insatiable appetite and Jigglypuff's ability to put enemies to sleep work together to defeat the wizard. Another idea is a story about a singing competition between them. Jigglypuff is known for its singing, but Kirby might surprise everyone with a unique musical talent of his own. They could learn from each other and become great friends through this competition.
Jigglypuff is often seen as a bit more vain about its appearance and talent compared to Kirby. In fanfiction, this could create an interesting contrast. Kirby doesn't really seem to care much about such things. So, Kirby could be the one to make Jigglypuff realize that there are more important things than just looking good and having a great voice. This could lead to a deepening of their friendship as Jigglypuff grows as a character thanks to Kirby's influence.
Perhaps a plot where they meet in a dream world and have to find their way back to reality. In this world, they discover new powers within themselves while also forging a stronger friendship. They could encounter strange creatures and solve puzzles to make their way back.