Who could be Waver's main rivals in a 'waver joins 5th holy grail war fanfic'?

One possible plot could be that Waver uses his intelligence to outwit the more experienced mages. He might form unexpected alliances, like with some of the Servants who see his potential. For example, he could team up with Rider to not just fight in the war but also to learn from him, growing as a mage and a person throughout the events of the Grail War.

Adventure is also a popular theme. Given Rider's capabilities, fanfic writers often send them on various adventures with Waver by their side. It could be exploring ancient ruins, battling powerful enemies, or seeking out magical artifacts. This allows for a lot of action - packed scenes and character growth.

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.

Sure. You can start by looking on some popular fanfic websites like Archive of Our Own. Just search for 'rider x waver' and you'll likely find a variety of stories written by different authors. Some might be adventure - themed, where Rider and Waver go on exciting quests together.

There were a few novels that met this requirement, such as Sword Immortal who joined the chat group, Infinity from the Giants, and The Final War of the Apocalypse. The protagonists of these novels were involved in the Holy Grail War, but the main content of the novels was not the Holy Grail War. It involved different worlds and storylines. If you're interested in these novels, you can read them. I hope you like my recommendations.

Overall, the waver design in One Piece manga is very creative. It helps to create a dynamic and visually appealing atmosphere. The way it's incorporated into the scenes makes the story more engaging.

The Waver blueprints might not have a direct connection to the One Piece manga. It could be something from a separate story or concept.

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.

Perhaps the story focuses on a previously unknown Master. This Master could be a young mage who accidentally stumbles upon the Grail War and has to quickly learn the ropes. They might form an unexpected bond with their Servant, like a Servant who is usually seen as cold-hearted but warms up to this inexperienced Master. This new dynamic could lead to a whole new set of adventures and challenges 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.