They could have a family. Imagine little dragon slayers or celestial wizards running around. Their children would inherit their strong magical powers and grow up in a loving family environment.
In the fanfiction, perhaps they face some challenges after getting married. Maybe there are issues with integrating their different magical abilities and how they use them in a combined way. But through love and understanding, they overcome these obstacles and their relationship becomes even stronger.
One great Sting and Yukino fanfiction is 'A Bond Beyond Guilds'. It delves deep into their relationship, showing how they support each other through various challenges in the magical world. The story has a great plot that keeps you hooked from start to finish.
Another theme could be adventure. They are both part of the Fairy Tail universe, so fanfictions may involve them going on quests together, facing challenges side by side, and growing closer through these experiences.
It's the chemistry between them. In the original story, there are hints of a special connection. Fanfiction writers take those hints and expand on them. For example, they can create scenarios where Sting and Yukino have to rely on each other completely, which is exciting to read. Also, fans like to see different sides of their personalities in these fanfictions.
The idea of a love story between them offers a different perspective on the Fairy Tail story. It gives fans a chance to explore a more romantic side of the world. Fanfiction writers can play with different tropes like forbidden love if they are from different guilds in the story, or they can write about how they support each other in their growth as mages. All these aspects combined make Sting and Yukino love fanfiction really appealing.
One interesting story could be where Sting and Yukino go on an adventure together in a magical forest. They encounter various mythical creatures and have to rely on each other's skills to survive.
In their married fanfiction future, they might travel the magical universe together. Discovering new spells and magical creatures. They could also become mentors to young students at Alfea, sharing their combined knowledge of magic and combat.
One idea could be that they discover the pregnancy during a mission. They then have to balance their duties as mages with preparing for the new life. Maybe they face some challenges from their guild mates who are initially worried about how it will affect their performance in the guild.
You can try looking on some popular fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions and you might be able to find some great Sting and Yukino stories there.
Sting would likely become more protective. He's always been a strong character, but now he has someone he truly loves and a child on the way. He might become more cautious in battles and less reckless. For example, he would think twice before taking on a very dangerous mission without proper backup.