Another way is to introduce a conflict within their relationship. Maybe Rook disagrees with one of Ben's decisions regarding the use of the Omnitrix. They have an argument, but then later realize that they both had valid points. This kind of internal conflict and resolution can make their relationship more complex and interesting.
By having them face a common enemy. When they fight side by side against a powerful foe, they can learn to trust each other more and understand each other's fighting styles better.
Another way is by showing their daily interactions. Like when they're just hanging out between missions, sharing stories about their different worlds. Ben could tell Rook about his adventures on Earth, and Rook could share stories about his Plumber training. This would make them understand each other better and grow closer. They could also have inside jokes that develop over time from these interactions. Also, having them train together to improve their combat skills would not only make them better fighters but also strengthen their relationship as they rely on each other during the training sessions.
One possible plot could be that Rook and Ben go on an adventure to a new planet in the Ben 10 Omniverse. They encounter a strange alien species that has a unique power. Ben tries to use his Omnitrix to transform into an appropriate alien to deal with the situation, but there are some glitches. Rook, with his Plumber skills, helps Ben figure out what's wrong and together they overcome the challenges and make new friends among the aliens.
There could also be a theme of self - discovery. As they interact, both rook and ben might discover new aspects of themselves. For example, rook might learn more about his own courage through his association with ben, and ben might understand the importance of loyalty better because of rook. This self - discovery can be a really interesting theme to explore in fanfic.
Friendship is a common theme. It could show how their friendship develops over different adventures in the Ben 10 universe.
First, understand the characters of Ben and Rook well. Their personalities should shine through in the fanfic. For example, Ben's more impulsive nature and Rook's calmness. Then, use the tickling concept in a creative way, like making it a unique form of communication between them.
Another theme is adventure. Since they are from a universe full of strange planets and creatures, many fanfics take them on exciting adventures across the galaxy. They might be searching for a powerful artifact or trying to stop an evil force from taking over the universe. It's all about the journey and the discovery along the way.
You can try looking on some popular fanfic websites like Archive of Our Own (AO3). It has a wide range of fan - created content, and there's a good chance you might find 'ben x rook lemon fanfic' there if it exists.
I'm not sure about specific rook x ben fanfic titles off the top of my head. But you could also check out some fanfic communities on social media platforms. People might share their favorite rook x ben fanfics there or even give you some tips on where to find them.
Another way is to follow some fanfic writers who are known for writing about these characters. They may post new 'ben x rook fanfic' on their personal blogs or on writing platforms. You can discover them through social media or by searching for Ben 10 fanfic writers.
An interesting aspect could be exploring Rook's past more deeply. Maybe he has some secrets from his time before being a Plumber that are related to the Ben 10 Omniverse. Ben could help him uncover these secrets while they are on a mission. For example, they could be investigating an ancient alien artifact, and as they dig deeper, Rook's past starts to unfold.