Well, the King Dedede weight gain story could be that he started eating a lot more of his favorite foods like big, juicy fruits and large cakes. Maybe he became a bit too fond of the luxurious feasts in his kingdom. As a result, he gradually put on weight. He might have noticed his clothes getting tighter and his movements becoming a bit slower due to the extra pounds.
One common theme is friendship. Female Dedede is often shown building strong bonds with other characters in the fanfic. For example, she might team up with a group of misfits to take on a powerful enemy.
One popular female Dedede fanfic could be 'The Adventures of Female Dedede'. It often features her in unique scenarios, like exploring a magical kingdom with her friends. The story might focus on her strength and leadership skills.
Definitely Naruto. Naruto would be curious about Kirby's abilities and would probably want to be friends right away. They could have some fun training sessions together, with Kirby showing off his inhaling skills and Naruto his new Rasengan variations. Also, Sakura might interact with Kirby. She could be initially a bit skeptical but would come around when she sees how Kirby can be helpful in medical situations by using his powers to quickly gather medicinal herbs or supplies.