Well, at first, Kurumu might be attracted to Gohan's power. But as they interact more, she realizes there's much more to him. Gohan, who has a strong sense of justice, could inspire Kurumu to be a better person. They could go on adventures together, facing challenges side by side. In the face of danger, they would rely on each other, and this mutual trust would strengthen their relationship. For instance, when fighting a powerful enemy, Gohan might get injured and Kurumu would have to step up and protect him, which would deepen their connection.
One plot idea could be that Gohan and Kurumu meet in a strange new world. Maybe they are both on a mission to save this world from a powerful evil. Along the way, they start to understand each other's strengths and weaknesses and develop a deep bond.
In a fanfic, their relationship could develop gradually. First, they might start with small exchanges of kindness, like Damian sharing his lunch with Anya when she forgets hers. Then, as time passes, they could be involved in a school play together. During the rehearsals, they get to know each other on a deeper level. Anya's telepathy might also play a role, for instance, she could use it to help Damian when he's in a tough situation at school, which would make him trust her more. This trust would be the foundation for their relationship to grow further into a real friendship or something more.
A common theme is the development of their relationship. Given their different natures in the Rosario + Vampire world, how they come to understand and care for each other is often explored. For example, Tsukune being a human and Kurumu being a succubus.
In a Gohan x Goku fanfic, their relationship can be delved into by creating scenarios where they have to rely on each other completely. For example, if they are in a situation where Goku's strength and Gohan's intelligence are both required to escape. Their different personalities can also be highlighted. Goku's carefree nature contrasted with Gohan's more studious and responsible side. And of course, flashbacks to Gohan's childhood and how Goku's presence or absence affected him can add depth to their relationship.
Another option is to check out some anime - themed forums. The fans there are usually quite passionate about the series and might have their own collections or recommendations of Tsukune and Kurumu fanfic. You could ask in a thread specifically dedicated to Rosario + Vampire fan works.
I'm not entirely sure if there is a specific 'Gohan x 18' fanfic. While the idea of pairing these two characters is interesting, not all fanfics are easy to find. Some might be on specialized fanfic websites, while others could be hidden in less - known corners of the internet. You could try searching on well - known fanfic platforms like FanFiction.net or Archive of Our Own, but there's no guarantee that you'll find one right away.
To develop their relationship, start with small moments of interaction. For example, Ayato could save Hinami from a dangerous situation, which would be the first step in building trust. Then, have them share their past experiences. Ayato could talk about his family and his struggles, and Hinami could do the same. This would make them understand each other better. Another way is to put them in a common goal - oriented situation, like working together to protect a group of weaker ghouls. Through this, they would see each other's strengths and weaknesses and grow closer.
One way is through dialogue. Fanfic writers use their conversations to show the evolution of their relationship. At first, their dialogues might be filled with snarky remarks and arguments. But as they get to know each other better, the tone changes. They start sharing their fears, dreams, and secrets. For example, Draco might open up about his insecurities regarding his family's reputation, and Ginny might share her own experiences of being in the shadow of her brothers. This sharing of personal thoughts helps in building a more realistic relationship.