You could add a young and naive ghoul who looks up to the Black Reaper as a mentor. This ghoul could be new to the world of ghouls and need guidance from the Black Reaper. Another potential character could be a mysterious old ghoul with vast knowledge of forgotten ghoul techniques. He could be an ally or an adversary depending on the situation. And a third character could be a human with psychic abilities who can sense the presence of ghouls. This human could befriend the Black Reaper or try to hunt him down.
A foreign ghoul with a unique set of powers could be added. For instance, a ghoul from a different culture might have powers related to elemental control. This would add an interesting dynamic as the Black Reaper has to deal with powers he's not familiar with. There could also be a female ghoul assassin who has been hired to kill the Black Reaper. She's highly skilled and has her own set of motives. And then there's the idea of a human scientist who is secretly studying ghouls. He could cross paths with the Black Reaper and try to use him for his experiments or help him understand his condition better.
It's quite intense and dark. The story and art are both compelling, keeping readers on the edge of their seats.
A merman could be one. He might be curious about the Black Sea Reaper and try to make friends or, on the contrary, see it as a threat to his underwater territory. Another could be a sea witch. She could have her own motives, either to help or to hinder the Black Sea Reaper. A young sea turtle could also be a character. It could look up to the Black Sea Reaper as a hero and follow it around on its adventures.
One idea could be exploring the Black Reaper's inner turmoil as he struggles between his human and ghoul sides more deeply. Maybe he has to make a choice between protecting a group of innocent humans or siding with a ghoul community that has shown him kindness. Another could be a time - travel plot where the Black Reaper goes back to a crucial moment in his past to change something, but discovers that changing the past has unforeseen and dangerous consequences. And a third idea could be a story where the Black Reaper teams up with an unlikely ally, like a human detective who is also trying to solve a mystery related to the ghoul underworld.
A young witch from a rival coven could be added. She might be initially antagonistic towards Ciel and Sebastian but later form an uneasy alliance when a greater threat emerges. She could bring in new magical elements and challenges to the story.
It's quite engaging. The plot is intense and the character development is compelling.
A young and curious wizard could be added. This wizard could be intrigued by the devil's unbreakable nature and try to study it, leading to some interesting interactions. Another character could be an angel who has lost its way and forms a strange bond with the devil. Or perhaps a talking animal, like a raven, that serves as the devil's confidant and gives it advice from a different perspective.
An American wizard detective. He could be investigating strange magical happenings in the wizarding world of America. The Potter character could cross paths with him and end up teaming up to solve a big case.
The Tokyo Ghoul Black Reaper Charter manga tells a tale of survival and power struggles. The main characters face off against various threats and uncover hidden secrets. It's full of action and mystery.
A mysterious old Pokemon trainer who has a lot of knowledge about ancient Pokemon moves. He could guide Rusty on his journey.
Potential new characters could include a fire mage with a dual personality. One personality is a calm and collected fire mage, while the other is a wild and uncontrollable one. Asta has to figure out how to deal with this character. There could also be a group of orphan fire mages that Asta takes under his wing. He trains them and they in turn, help him in his battles with their unique fire magic abilities. Additionally, a mysterious old man who is a master of a forgotten form of fire magic. He sees potential in Asta and decides to pass on his knowledge to him.