You can find 'rottmnt leo x usagi fanfiction' on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fan - made stories, and you can easily search for this specific pairing.
Some 'rottmnt leo x usagi fanfiction' that are worth checking out include 'The Hidden Connection'. In this story, Leo and Usagi discover a mysterious link between their two worlds that only they can understand. The fanfiction 'The Duo's Destiny' is also quite good. It takes them on a journey where they must fulfill a prophecy together, and along the way, their relationship deepens in a very heartwarming way.
You can start by looking on fanfic websites like Archive of Our Own (AO3). Use the search function and type in 'ROTTMNT Don x Leo' and then filter out any NSFW tags. Another option is Fanfiction.net. There, you can also search for the characters and then manually skim through the results to avoid any inappropriate stories.
One idea could be a story about Don and Leo teaming up for a scientific discovery in the sewers. They could face some challenges together, like malfunctioning tech and strange mutant creatures. Another idea is a story where they have to rescue their other brothers and their teamwork and unique skills are highlighted.
Leo's reaction could be complex. He would likely be frightened, but also angry that Marcus would do such a thing. He might use his wits to try and outsmart Marcus. For example, he could pretend to be more scared than he actually is to make Marcus let his guard down. He could also try to find something in the kidnapping location that he could use as a weapon or a tool to escape. As the situation drags on, he may start to worry about how his friends, the Lab Rats, are doing and if they'll be able to find him in time.
Their friends might be initially shocked. But then, some would be really excited and start planning for the baby's arrival. For example, they might start knitting baby clothes or building a nursery. Others could be a bit worried, especially if they think Leo and Reyna are not ready for this big step.
The more open - minded friends like Grover could be immediately supportive. Grover might see the love between Leo and Percy and be happy for them, maybe even helping them deal with any negative reactions from others.
Raph usually gets really angry. He blames himself for not being there to protect Leo or he gets mad at the enemy who hurt Leo. He'll be the first to want revenge and will be very protective of Leo while he's injured.
A great 'rottmnt crossover fanfic' has well - written characters. It should stay true to the original personalities of the 'rottmnt' characters while also adapting them to fit into the new crossover universe. For example, if they cross over with a magical world, their reactions and how they use their skills should be believable.
Raph would be the first to show his concern through anger. He'd be mad at himself for not protecting Leo better and also at the situation that led to Leo's injury. Mikey would be visibly distraught, constantly by Leo's side trying to cheer him up. Donnie would be all business, using his scientific knowledge to figure out the best way to treat Leo's wounds and help him recover.