Well, Caster can be considered an interesting secondary character. He has his own brand of magic and his actions often disrupt the flow of the Grail War in unexpected ways. Also, Lancer is quite captivating. His loyalty and the code of honor he follows, even in the chaotic Grail War, add an interesting dimension to the story.
There are several. Kirei Kotomine is a character that's hard to ignore. His moral ambiguity and his role as a sort of observer and manipulator in the Grail War make him very interesting. And then there's Sakura. Her quiet and somewhat reserved nature, yet her importance to the overall plot, especially in relation to Rin, makes her an engaging secondary character.
I'm not sure if there is a specific visual novel with exactly that scenario in the mainstream market. There are many visual novels out there, but this particular combination might be rare or not exist in a non - adult - themed context.
The main storylines often revolve around the complex relationships between the characters. For example, the relationship between Saber and Rin is central. Saber, with her noble and chivalrous nature, and Rin, who is intelligent and strong - willed, have interactions that drive the plot. There are also elements of magic, battles, and the exploration of different fates within the story.
There could be a mage character who acts as a guide or ally to Saber. Maybe there's also an antagonist, like a dark knight or a powerful sorcerer.
Shino is often an interesting secondary character in Naruto fanfiction. His ability to control bugs gives a unique aspect to stories. Writers can explore his more introverted nature and how it affects his relationships with other characters. Another one is Rock Lee. His determination and unique fighting style can be the focus. In fanfiction, his story can be expanded on, like his training methods and how he overcomes his limitations.
There could be other Vocaloid characters. For instance, her brother Kagamine Len might be a main character. They often have a special bond and their interactions can be a significant part of the story.
Yui is quite an interesting secondary character. Her cheerful personality contrasts with Hachiman's cynicism and Yukino's coldness, and she often acts as a mediator between them.
It's hard to say without reading it thoroughly, but perhaps there could be a detective - like character who is trying to uncover the secrets of Izaya and Namie. This character would add an element of mystery and suspense.
One interesting secondary character could be their classmate who is always getting into comical situations. This character might add some humor to the story and also serve as a contrast to the more serious or deep - thinking Hirano and Kagiura. For example, when Hirano and Kagiura are having an intense conversation about their future plans, this classmate might barge in with a silly problem, like losing their lunch box.
Saber is often a symbol of honor and power, and in relation to Rin, they can be written in fanfiction as two characters who grow to understand and respect each other more. Rin's knowledge of magic can be a key factor in their interactions. However, when it comes to lemon fanfiction, it's not a proper area to explore their true characters as it usually involves vulgar content.
Snape is an extremely interesting secondary character for fanfiction. His double - agent role and his complex feelings towards Lily Potter can be explored from different angles. There are fanfictions that focus on his early years at Hogwarts, his relationship with the Marauders, and how all of that shaped him into the man he became. Another character is Cho Chang. Her relationship with Harry can be re - examined and extended in fanfiction, and she can also be given more depth and backstory outside of just her romantic connection to Harry.