Some excellent characters for Birdy the Mighty Crossover fanfiction are Lelouch from Code Geass. His strategic mind and his complex personality would add depth to the story when combined with Birdy. Also, Asuna from Sword Art Online. Her combat skills in a virtual world and her strong will could lead to great team - up moments with Birdy. And don't forget about Ichigo from Bleach. His ability to see spirits and his powerful sword - fighting skills could make for some exciting crossovers with Birdy in different scenarios.
One idea could be to crossover Birdy with a popular mecha anime. Picture Birdy in a Gundam-like universe, fighting side by side with giant robots. Another could be a crossover with a magical girl anime, where Birdy has to learn some new magical powers to save the day. Or perhaps a crossover with a detective anime, and Birdy uses her skills to solve complex mysteries in a new setting.
Obviously, Birdy herself is a very popular character to focus on. Her dual nature as an alien and her life on Earth make for a lot of interesting storylines. Tsutomu is also a key character. His relationship with Birdy, from being initially shocked to gradually becoming her partner, is full of potential for fanfiction.
If it's a crossover with Star Wars, characters like Luke Skywalker and Darth Vader would be great. The Power Rangers could get involved in the fight between the Jedi and the Sith. Maybe the Rangers' morphing powers could be related to the Force in some way.
One interesting plot idea could be a crossover with another popular anime where the characters from Birdy the Mighty Decode have to team up with the new characters to face a common enemy. For example, if they cross over with Naruto, Birdy and her allies could join forces with Naruto and his friends to battle a powerful alien threat that is too much for either group alone.
One idea could be exploring Birdy's life before she came to Earth. Maybe she had a special mission on her home planet that was interrupted and how that might still affect her actions on Earth. Another could be a 'what if' scenario where Birdy and Tsutomu's relationship took a different turn from the start, like if they were more antagonistic towards each other initially.
In a Dorohedoro crossover with 'One Punch Man', Saitama would be an interesting addition. His overpowered nature would contrast with the often - more - gritty and complex power levels in Dorohedoro. Another good character could be Guts from 'Berserk'. His dark and brooding personality would fit well in Dorohedoro's gloomy atmosphere. Also, Edward Elric from 'Fullmetal Alchemist' could bring his knowledge of alchemy and his quest for truth to the Dorohedoro world.
In vegito crossover fanfiction, characters like Jiren would be great. His strength and stoic nature would make for some intense interactions with Vegito. Also, Android 18 could be included. She has her own unique set of powers and a strong will. Her presence could add some interesting dynamics, especially if she has to team up with Vegito against a common enemy. And don't forget Frieza. His evil nature and thirst for power always make for an exciting addition to any Dragon Ball - related story.
Kenny McCormick (Mysterion) could cross paths with Batman. Batman's detective skills and high - tech gadgets would make for an interesting dynamic with Mysterion's more 'underground' superhero style. They could work together to solve a mystery that spans Gotham City and South Park.
For a crossover with Doctor Who, the Doctor could be an interesting addition. He could bring his time - traveling abilities and vast knowledge to the Shadow World. And from the Shadowhunter side, Jace Wayland would be a good character to include. His charm and combat skills would make for some interesting dynamics with characters from other universes.
For a crossover with a post - apocalyptic world, characters like Mad Max could be involved. He might see the homunculi as either allies or threats in the harsh new world. In a crossover with a cyberpunk world, characters like Neo from 'The Matrix' could be interesting. The homunculi could be part of the complex digital and physical world that Neo navigates, and he could help them understand the true nature of their existence in this new, high - tech world.