Arcueid Brunestud, with her vampire - like powers and her own complex backstory, could also be a great character to include in a crossover. Her powers could interact in interesting ways with characters from other franchises, and her story could add more depth to a crossover fanfiction.
You could also consider a crossover with a detective - based series like 'Detective Conan'. The mystery - solving aspect of 'Detective Conan' could be combined with the complex and often mysterious events in 'garden of sinners'. The characters from both could work together to solve cases that involve both the normal and the supernatural.
If we consider a crossover with 'Naruto', Naruto himself would be an interesting character to include. His never - give - up attitude and his powerful ninja abilities would make for some exciting scenarios. He could form a friendship with the Railgun characters and teach them some of his ninja skills, or they could teach him about their esper powers.
Sora from Kingdom Hearts could be a fun addition. His positive attitude and his ability to use keyblades and magic would be a different take in the dark Castlevania setting. He could bring a sense of hope and light to the story. Also, Cloud Strife from Final Fantasy VII. His Buster Sword skills and his experience in fighting against powerful foes like Sephiroth could translate well in the battles against the lords and demons in Castlevania Lords of Shadow. His stoic personality would also create an interesting dynamic with the more emotional characters in the game.
In a crossover with the Metal Gear series, Snake would be a great addition. His stealth and combat skills are on par with the Ghosts. He could bring in his unique gadgets and knowledge of espionage.
You could include characters like Naruto from 'Naruto'. His ninja skills and determination would make for an interesting dynamic with the Persona 4 characters. Also, characters from 'One Piece' like Luffy. His carefree yet strong - willed nature would contrast well. And of course, characters from 'Sword Art Online' like Kirito. His sword - fighting skills and experience in virtual worlds could add a new dimension to the fanfic.
The main character is Shiki Ryougi. She has a distinct personality and abilities that drive much of the story.
In my opinion, Shiki Ryougi is really fascinating. Her past and her special ability to see death lines make her a unique character. She has a complex personality that is shaped by her traumatic experiences. Then there's Fujino Asagami. Her power and her struggle with her own nature are quite captivating. Also, Tomoe Enjou is an interesting character as he is involved in some of the most mysterious parts of the story.
From the Resident Evil franchise, characters like Leon S. Kennedy or Jill Valentine would be great. They have experience with fighting bio - organic threats, similar to the infected in Left for Dead. Their combat skills and knowledge of survival in a world overrun by monsters could blend well with the Left for Dead characters. They could exchange tactics and weapons, and together face new challenges that neither group has seen before.
You could include characters like Naruto. His ninja skills and the Shield Hero's combat style would create an interesting dynamic. Also, characters from One Piece such as Luffy. Their different leadership styles and goals would be fascinating to explore in a crossover. Another suitable character could be Harry Potter. The magic in the Harry Potter universe and the Shield Hero's abilities could interact in unique ways.
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.