Perhaps there's a plot where an outside force, like a new business rival, tries to drive a wedge between Mr. Burns and Smithers. But instead of succumbing to the pressure, they work together to overcome the obstacle and in the process, their bond becomes stronger than ever.
One idea could be that Smithers finally decides to confess his true feelings to Mr. Burns in a very emotional moment. Maybe after saving Mr. Burns from a dangerous situation at the power plant.
A new assistant hired by Mr. Burns who is jealous of Smithers' position could be the main antagonist. This new character might try to undermine Smithers at every turn.
One popular Burns Smithers fanfic could be about their relationship in a different work setting, like if they were in a modern startup instead of the Springfield Nuclear Power Plant. Another might explore what would happen if Smithers finally got the courage to confess his true feelings in a really emotional way.
Perhaps a fanfic where Ryoba Aishi discovers a secret about Mr. Saikou's family that puts them in a difficult situation. They must then rely on each other to keep the secret and in the process, their relationship deepens. It could involve mystery, intrigue, and a lot of character development.
One idea could be a story where Leon and Mr X are forced to team up against a common, even more dangerous enemy. Maybe a new virus strain creates mutants that are a threat to both of them.
Archive of Our Own (AO3) is a great place to start. It has a large collection of fanfics on various topics, including Burns Smithers ones. The site has a good search function that allows you to easily find what you're looking for.
It's kind of complicated. Sometimes they have a working relationship, sometimes there's a hint of something more.
The OC could be a therapist who is assigned to treat Elliot. At first, Elliot is very resistant to the idea of therapy. However, the OC is persistent and gradually breaks through his walls. As they interact more, the OC starts to understand Elliot's complex mind and the world of hacking he is involved in. This leads to a romantic connection as the OC becomes a part of Elliot's world and helps him in his fight against Evil Corp.
I have no definite idea. It might be a comic that focuses on the humorous and unexpected situations involving these characters and the blushing element adds an extra layer of intrigue.
One idea could be a crossover where Naruto's world and the world of X - 23 from the X - Men collide. Maybe X - 23 is on a mission and accidentally ends up in the Hidden Leaf Village. She has to learn to adapt to this new place with its different culture and ninja ways. Naruto could be intrigued by her and her abilities, and they could team up to face a common enemy.
One idea could be a story where Spiderman has to team up with his greatest enemies to fight a new, more powerful threat from outer space. This would force him to put aside his differences and find common ground with the likes of Doctor Octopus and Green Goblin.