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 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.
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.
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.
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.
Another theme might be adventure. They could be on a journey through a magical forest or some other fantastical setting, facing various challenges together. This gives a lot of room for action and excitement in the stories. Also, there could be themes related to self - discovery. As they interact, they might learn more about themselves and their own capabilities. For example, the wolf might discover a more gentle side of himself, and the snake might find that he can be more social than he thought.
By creating complex characters. For example, give Leon some internal conflict related to his past experiences with bio - organic threats like Mr. X. Maybe he has nightmares about his previous encounters and this new interaction with Mr. X stirs up those memories. For Mr. X, add some sort of mystery about its true purpose beyond just being a killing machine. This will make the readers more engaged as they try to figure out the characters' motives and secrets.
Well, you can try looking on some popular fanfiction websites like Archive of Our Own. Just search for 'mr wolf x mr snake' there, and you might find a good selection of stories.
Mr. Burns might try to take care of him. Despite their strange relationship, Burns could feel some sense of responsibility or concern for his loyal assistant.