The reader could be a member of a rival group to Ayato's. At first, they are enemies, constantly trying to outdo each other. But during a common mission or task, they realize they have more in common than they thought. Ayato and the reader then have to navigate their new - found understanding while also dealing with the expectations of their respective groups.
Incorporate some unique elements. For instance, if there's a special event in the world of Ayato Kirishima, like a once - in - a - lifetime festival. Have the reader and Ayato attend it together. This gives you a chance to explore new aspects of their relationship. Also, add some humor. Maybe the reader tries to cook for Ayato but it turns out horribly, and Ayato's reaction can be both funny and endearing. This mix of different elements will make your fanfiction more engaging.
One possible analysis could be that their relationship in fanfic often showcases a strong bond of friendship. Bakugo's explosive personality and Kirishima's more stable and friendly nature create an interesting dynamic. Fanfic writers may explore how they support each other during battles or in their daily lives at school. For example, Kirishima might be the one to calm Bakugo down when he gets too riled up, and Bakugo could inspire Kirishima to be more confident in his abilities.
Kirishima is still alive in the manga. The story doesn't have that plot point. Usually, character deaths are significant events and are clearly shown if they occur.
Ayato in Diabolik Lovers is often portrayed as confident and somewhat possessive. In Ayato x Reader fanfictions, his character traits are usually amplified. He's shown to be highly attracted to the reader and will go to great lengths to keep them close. His vampire nature also adds an element of danger, as he may struggle with his blood - thirsty instincts while being in love with the reader.
Another characteristic is the exploration of his relationships. His friendship with Bakugo is a popular theme. Fanfics might show how they support and challenge each other. Also, his relationships with his other classmates are often explored, like how he can be a source of motivation for them.
Kirishima is from a manga/anime. His back story involves him having a sense of self - doubt initially. He admired those with strong and manly qualities. He worked hard to overcome his insecurities and develop his own strength and courage, eventually becoming a reliable hero - in - training.