A young master who is a novice but has an exceptional ability to communicate with servants could be a main character. They might be able to form bonds with multiple servants, which is unusual in the Grail War. Their servants could include a mix of different types, like a mage - type servant and a warrior - type servant. Also, an old and experienced master who has participated in previous Grail Wars and has a vendetta against a certain group could be a main character. His servant could be a servant with a dark past that parallels his own.
One of the main characters could be a servant who is not from the normal pool of heroic spirits. Maybe they are a 'wild card' servant created by some unknown magic. Their master could be a young girl who is pure of heart but has no prior knowledge of the Grail War. This combination of an unknown servant and an inexperienced master would create a lot of interesting situations as they try to figure out the rules and compete against the other 49 servants and their masters in the Grail War.
The main characters could include a master who has a hidden past and a powerful servant. For example, a master who was once part of a secret organization related to the Grail War but lost their memory. Their servant could be a heroic spirit known for their combat skills, like Artoria. Another possible main character could be a servant who has their own agenda different from the other servants, such as a servant who wants to use the Grail not for the traditional wishes but to change the very nature of the Grail War itself.
One possible plot could be that with 49 servants, the Grail War becomes extremely chaotic. There could be multiple alliances and betrayals among the masters and servants. Maybe some servants with unique abilities form a group to try and change the rules of the Grail War, as they realize that with so many participants, the traditional way of winning the Grail might lead to too much destruction.
Servants are also often main characters. For instance, Saber, with her noble and powerful presence. In the fanfic, she might have different relationships with other characters compared to the original. Her backstory and her connection to the Grail War are important elements that make her a main character.
A Servant could be a famous inventor from history, like Nikola Tesla. His abilities could be related to electricity and innovation. He could create powerful electric fields or develop new weapons on the spot using his knowledge. Another unique Servant could be a mythical sea creature, like a Kraken. It could have the power to control water and summon other sea monsters to do its bidding.
Archer is often quite popular. His complex personality and his various abilities make him a great character to explore in reaction fanfiction. His snarky remarks and his hidden depths can be really interesting to write about in different reaction scenarios.
Shirou is obviously a main character. Often, Saber would still be a major part as well, since she has a strong connection with Shirou in the original story. Other Servants and Masters from the original Holy Grail War concept might also appear.
The characters included the male protagonist, Arther, a reborn wizard with memories of two different worlds, the female protagonist, Nicole, the unknown male supporting character, Urrezo, a terrifying wizard, the mysterious Seven Stars, and the male supporting character, the God of April, an old god with a mysterious origin. "The Fifth Holy Grail" was written by Yu Qingyu. It was a sci-fi/interstellar civilization novel. It had been completed and could be enjoyed without worry. [User recommendation: Knowledge is power. For the sake of knowledge, wizards contribute everything they have.] I hope you will like this book.
One could be a young female mage as the main character. She might be from a family that has been on the outskirts of the mage society and is trying to prove herself in the Grail War.
Kotomine Kirei could be one of his main rivals. Kirei has a complex and devious nature, and his experience in the Grail War would make him a formidable opponent for Waver. Another could be Tohsaka Rin. She is a skilled mage, and her determination to win the Grail would put her at odds with Waver.
I'm not sure specifically as it depends on the fanfic, but common servants in the Ciel universe might include Sebastian. He is a very important servant to Ciel and often plays a crucial role in many situations.
Miku could be a central character. She's one of the most well - known Vocaloids, and she could be leading the fight against an evil force trying to take over the Vocaloid realm.