In a crossover with My Hero Academia, characters like All Might could be included. His sense of justice would make him an interesting counterpart to Devilman. He could be initially skeptical of Devilman's powers but then come to respect him as they fight together against a villain that combines the traits of demons and quirks.
If it's a crossover with Fullmetal Alchemist, Edward Elric would be a great addition. His scientific knowledge and his search for the Philosopher's Stone could intersect with Devilman's world. Maybe he could try to find a way to reverse the demon transformation using alchemy, leading to an interesting dynamic between them.
For a crossover with One Piece, Luffy would be an exciting character to include. His carefree nature and strong will would contrast with Devilman's more brooding personality. They could embark on a journey together, with Luffy seeing Devilman as a new and powerful friend, and Devilman being intrigued by Luffy's Devil Fruit powers and the concept of the Grand Line.
One idea could be a crossover with Neon Genesis Evangelion. Devilman and the Eva pilots could team up to fight a common enemy that threatens both their worlds. Maybe a new type of demon that has the ability to control Angels.
Akira is definitely one of the most interesting. His transformation into Devilman and his internal struggle make for great writing material. Ryo is also fascinating as his true nature and his actions throughout the story give a lot to explore. And Miki, with her kindness in the midst of all the chaos, can be really interesting to write about in different scenarios, like how she copes with the truth about Akira.
One great Naruto and Devilman Crybaby fanfiction is 'The Crossover Chronicles'. It combines the unique powers and worlds of both series in an interesting way. The characters from Naruto, like Naruto himself and Sasuke, interact with the complex characters from Devilman Crybaby, creating new storylines and character developments.
You can combine the characteristics of characters from both franchises. For example, if you're crossing with One Piece, take the Devil Fruit powers and combine them with the demonic powers in Devilman Crybaby. A character could have the power of a Zoan - type Devil Fruit and also be a Devilman, having the ability to transform into a powerful hybrid form.
Another plot idea is to crossover with Neon Genesis Evangelion. The Angels in Evangelion could be some sort of new form of demons in the Devilman Crybaby universe. The Eva pilots might have to team up with Devilmen to fight these powerful threats. It could explore the psychological aspects of both universes as the characters deal with the new and terrifying situation.
One popular theme is the exploration of the complex relationships between the characters. For example, the relationship between Akira and Ryo is often delved into more deeply in fanfiction. Another theme could be the alternate versions of the story's events, like what if certain battles had different outcomes. Also, the inner turmoil of the characters, such as Devilman's struggle with his dual nature, is a common theme in fanfiction.
In this fanfiction, perhaps it delves into the emotional connection between Akira and Miki. Akira's transformation into Devilman could add a lot of drama to their relationship. Miki might be the one who tries to understand Akira's new self, and they could go through a journey of self - discovery together.
In a crossover with Devil May Cry, Dante would be a great addition. His cocky and powerful attitude would contrast well with the more brute - force nature of the Splatterhouse protagonist. They could team up to fight some sort of demonic invasion that threatens both of their worlds.
There is also 'Devilman Crybaby: A New Dawn'. This fanfic focuses on what could have happened if the events at the end of the series had a different outcome. It's a really creative take as it imagines a world where some of the main characters make different choices, leading to a whole new set of adventures and challenges.
Storm from the X - Men would be a great addition. She has control over the weather, which could create some really interesting scenarios when combined with Wolverine's combat skills. For example, she could create a lightning storm while Wolverine battles enemies in the rain, using the flashes of lightning to his advantage.