Maybe a rogue mutant. There are all kinds of mutants in the TMNT universe. One that has a grudge against the Turtles or just wants to use Donatello's skills for their own gain could be the kidnapper.
Well, perhaps a new villain who has heard of Donatello's genius kidnaps him to use his brainpower for some evil scheme in the underworld. Donatello might be able to use his wits while in captivity to leave clues for his brothers. And his brothers, once they realize he's missing, would start scouring the city, interrogating informants and following leads to find him.
One possible analysis could be that their relationship in fanfiction often explores a deep bond. Maybe it delves into how their different personalities, Donatello's intelligence and Raphael's brashness, interact and complement each other. It could also show their growth as characters through their relationship, like learning to understand and support one another better.
A possible plot twist could be that April is pregnant, but it turns out that there was some sort of mix - up or false positive. This would cause a great deal of emotional turmoil for both of them. They would have to deal with the disappointment and also re - evaluate their relationship and future plans.
One idea could be that they face challenges in a world that is not fully accepting of their relationship. They might have to deal with the reactions of their friends and family. For example, some of their friends could be initially shocked but then gradually come to support them. The fanfiction could focus on how they grow together as a couple during the pregnancy, learning about each other's fears and hopes.
A 'dark Donatello' fanfiction might explore the idea of him being an outcast among his own kind. Maybe he discovers a dark secret about his origin that makes him question his place in the world. This could lead to him becoming bitter and angry, and his actions would be different from the usual heroic Donatello. For example, he might start to isolate himself and work on projects that are considered unethical by his family.
Love and attraction is another common theme. Writers like to explore the budding romance between them. It could be a slow - burn kind of love where they gradually realize their feelings for each other. Sometimes it's shown through their small gestures and glances.
In fan fiction, 'Donatello sneezed' could be the start of an interesting plot. It could lead to other characters' reactions. Some might be concerned if he's getting sick, or it could start a chain of events. For instance, if he sneezes during a delicate experiment he's conducting, it could cause a minor disaster. Or perhaps his sneeze has some sort of magical or unexpected consequence in a fantasy - based fan fiction world.
One of the common themes is mutual respect. In fanfiction, they often come to respect each other's skills and abilities. Also, the theme of loyalty is prevalent. They stand by each other through tough times. For example, when one of them is in danger, the other will go to great lengths to save them. Additionally, the theme of brotherhood is often explored, highlighting their connection as part of the same team.
One of the main events was his apprenticeship under Ghiberti. This was crucial in his development as an artist. Another was the creation of his famous 'David', which was a milestone in Renaissance sculpture. He also received many commissions from wealthy patrons in Florence, which allowed him to produce a large body of work.