It could be the result of a parallel universe scenario. In a different dimension, Robin might have had a very different upbringing or set of experiences. If, for some reason, that version of Robin crosses over into the Young Justice universe, his 'evil' nature could disrupt the team. He might be more ruthless, more self - centered, and not care about the well - being of others as the normal Robin does.
He could be influenced by an ancient evil artifact. There are often such items in fanfiction universes. If Robin comes into contact with it, the artifact's dark power might corrupt him, changing his values and turning him against his friends.
If Robin is constantly underestimated and not given the respect he thinks he deserves within Young Justice. He might grow bitter and resentful. Over time, this negative emotion could fester and turn him evil. He could start to see his teammates as obstacles rather than friends and begin to plot against them.
One possibility could be that he's brainwashed. Maybe a powerful villain uses some mind - control device or magic to turn Robin against his friends. In fanfiction, this could lead to some really intense battles where his former teammates are reluctant to fight him at first, but realize they have no choice.
A new super - villain group that wants to take over the world might be behind it. They figure that by experimenting on Robin, they can learn the secrets of the Young Justice and use that knowledge against them. Or perhaps an old enemy of Batman who wants to get back at him by harming his protege.
First, you need to do some research on Robin's character in the Young Justice universe. Know his strengths, weaknesses, and relationships. Then, when writing about him being sick, describe his symptoms vividly. It could be something like a high fever that makes his vision blurry or a cough that won't go away.
Slade could be the kidnapper. He has a history of being an adversary to the Teen Titans, and in a Young Justice context, he might target Robin for his skills and connections. He would likely have a well - thought - out plan to use Robin for his own dark purposes, maybe to gain access to some secret information or technology that Robin has knowledge of.
There's also a chance that it could be a rogue member of a hero organization. They might have gone bad and decided to kidnap Robin for some self - serving reasons, like trying to gain power or access to certain secrets within Young Justice.
It could mean that Robin is physically exhausted from all the missions in the Young Justice universe. Maybe he's been on back - to - back operations, fighting bad guys and staying up late to plan strategies.
His teammates are very likely to be the ones to save him. Aqualad, with his leadership skills and water - based powers, could find a way to get Robin out of a dangerous situation. He might use his strategic mind to outwit the threat and rescue Robin.
Often, they interact with a lot of banter. Robin is quick - witted and Artemis is sharp - tongued, so their exchanges can be really fun to read. For example, Robin might make a smart - aleck comment about Artemis's aim, and she'll fire back with a jab about his detective skills.
Well, in this fanfiction, perhaps Robin left because of some misunderstanding with the team. The Young Justice team then starts to recall all the great things he did for them. They search everywhere, from Gotham to other far - flung places. They might even encounter new allies or enemies during their search for Robin. As they get closer to finding him, they also start to resolve the issues that led to his departure in the first place.
In a Young Justice Robin Cereal Fanfiction, the plot could revolve around Robin having a bet with his teammates about who can finish a large box of a really difficult - to - eat cereal first. But as they start the bet, they realize that there are strange things happening around the cereal. Like, it seems to be attracting small, strange creatures. So they have to stop the bet and figure out what's going on with this cereal before it causes more trouble.