To develop the character of Jessie, start with her backstory. Decide where she came from, how she became a vampire. Maybe she was turned against her will by an evil vampire. Then focus on her personality traits. Is she shy? Outgoing? You can also show her relationships with other characters. For example, how she interacts with the kids she babysits, whether she's strict or more like a fun big sister.
One plot idea could be that the Jessie OC has a special power that is hidden from the other vampires. For example, the ability to see the future which she uses to protect the family she babysits for from impending vampire threats. Another idea is that she is from a different vampire clan and has to keep it a secret while babysitting, and there could be a conflict when members of her clan come looking for her.
Their relationship could develop through mutual support. Since they are having a baby together, they would need to be there for each other. For example, Luke could be there for Jessie during her morning sickness.
First, think about your OC. Decide on their personality traits, like if they're brave or shy. Then, consider how they'll fit into Jessie's world. For example, are they an enemy turned ally? Next, plan out a basic plot. It could start with a simple meeting between your OC and Jessie.
For Jessie, you can develop her by showing her growth in terms of her relationships. If she's shy at first, show how she becomes more confident around Tony and the other Jessie. Tony can be developed by giving him a backstory. Maybe he has a troubled past that makes him more empathetic towards the Jessies. The other Jessie can be developed by highlighting her differences from the first Jessie. For example, if one Jessie is more artistic, the other could be more scientific, and show how they learn from each other.
Develop a unique backstory for the OC. Maybe they were turned into a vampire against their will by an evil vampire lord. This would give them a motivation to fight against injustice within the vampire community. Their backstory could also be tied to the babysitter vampire in some way, like they share a common enemy from their past.
First, think about their backstory. For example, if they're a vampire, were they turned recently or centuries ago? If they're human, what led them to Yokai Academy? This backstory will influence their personality. Also, give them unique traits. Maybe they have a strange phobia or an amazing talent like being able to communicate with spirits. Their relationships with the existing Rosario Vampire characters are crucial too. Do they immediately get along with Tsukune or do they clash with Moka at first? These interactions will shape their character as the story progresses.
Yes, there are likely many out there. You can start by looking on popular fanfiction websites like Archive of Our Own. Just search for 'Jessie Luke and Jessie kiss' in the search bar, and you should be able to find relevant stories. However, the quality can vary greatly, so you might have to read through a few to find one that really suits your taste.
You need to create a vivid setting. Since they are toys, you could describe their toy box or the playroom in detail. Use descriptive language to bring the story to life. For the relationship aspect, show their growing closeness gradually. Maybe they start by arguing over how to handle a situation but end up relying on each other more and more. Also, don't forget to add some conflict, like a jealous toy trying to come between them.
Ash is usually very positive and determined. In Jessie's body, he might try to bring some of that positivity to Team Rocket, which would be a big change for them. Jessie, on the other hand, is more devious and cunning. In Ash's body, she might be more aggressive in Pokémon battles, using strategies that are a bit more underhanded at first until she realizes that Ash's way also has its merits.
You can try fanfiction websites like Archive of Our Own or FanFiction.net. They usually have a wide range of fanfictions, including those about Jessie.