His friends, like Caleb. Caleb could bring in different dynamics to the story. His loyalty or possible betrayals can create interesting twists in the fanfic.
Nick himself is obviously a must - include character. His character is central to the whole concept of the Chronicles of Nick.
The villains or antagonists from the original Chronicles of Nick also make for great inclusions. They can drive the conflict in the fanfic, making it more exciting. For example, a powerful dark sorcerer who constantly tries to thwart Nick's plans.
A character like Hermione from the Harry Potter series could be great. Her intelligence and magic knowledge could pair well with Nick. Also, Batman. His detective skills and resources could create an interesting dynamic with Nick. And of course, Aragorn from Lord of the Rings. His leadership and combat skills would add a lot to the story.
Harry Potter himself is still very popular in fanfics. Writers often explore different sides of his character, like his post - war life or his relationships in more detail. Hermione Granger is also a favorite. She's often given more complex storylines, such as leading a magical research project. Draco Malfoy is another one. Fanfic authors like to redeem his character and show his growth and change over time.
The main character from the game, of course, is a popular choice. Also, Cyrus from Team Galactic is often included as he is such a complex and interesting villain. And Dawn or Lucas, depending on the version, are great to have as they are the typical Pokemon trainers that players can relate to.
Sebastian is often a popular choice. His demonic nature and his loyalty (in a rather twisted way) to Ciel make him a very interesting character to cross over. He can easily interact with characters from other dark or supernatural works, and his powers and suave personality can add a lot to a crossover story.
Pikachu is always a popular choice. It's so well - known and cute, and imagining it in a transformation scenario, like turning into a human or another Pokemon, can be really interesting. Another popular character would be Charizard. Its cool and powerful look makes for great transformation stories. And of course, Mewtwo. Given its mysterious origin and powerful psychic abilities, a TG story involving Mewtwo could be very engaging.
In Pokemon, Pikachu is always a popular choice. It's the mascot of the franchise and super recognizable. In Digimon, Agumon is really popular. So including them in a fanfic would draw a lot of readers. Also, characters like Ash from Pokemon and Tai from Digimon are well - loved and would be great to have in a crossover fanfic as they could lead the combined adventures.
SpongeBob SquarePants is definitely a popular choice. His goofy and positive nature can add a lot of humor to the story. Also, Danny Phantom is a great addition as he has cool powers and a heroic personality. Another popular character is Timmy Turner. His fairy - godparents can bring in some magical elements to the fanfic.
Knuckles would be a great addition. His strength and his role as the guardian of the Master Emerald can add a lot of depth to the story. He could have some interesting interactions with Coldsteel, perhaps even getting into a friendly rivalry. Also, Shadow could be included. His dark and brooding nature would make for an interesting dynamic with Coldsteel.
Rimuru Tempest is an obvious choice as he is the main character in the original series. He has a lot of potential for further development in fanfics. Veldora is also popular. His powerful dragon form and his comical personality can add a lot of fun elements to the story. And Shizu, her backstory and connection to Rimuru make her a great character to include.
Well, aside from the main trio of Charlie, Alastor, and Angel Dust, Husk is becoming a popular character to include. His grumpy and alcoholic nature can provide some comical relief in crossovers. Niffty is also a great addition. Her hyper - active and somewhat naive personality can be a contrast to more serious characters from other crossovers. And let's not forget Lucifer, who can bring a whole new level of power and mystery to the crossover fanfic.