One common theme is the growth of the characters. As they babysit, they learn more about themselves and become more responsible. Another theme is friendship. The babysitters form strong bonds with each other while taking care of the kids.
You can try looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfics from various fandoms, including 'gakuen babysitters'. Another option is FanFiction.net, which also has a wide range of fan - created stories.
One idea could be a fanfic where the babysitters have to deal with a group of new students who are very mischievous. Another could be a story about the babysitters' own pasts and how it affects their current babysitting roles. Maybe a fanfic where they take the kids on an unexpected adventure outside of the school campus.
Another option is Archive of Our Own (AO3). It has a large collection of fanfictions. When it comes to 'gakuen babysitters fanfiction', you can find ones that take the original plot and give it a unique twist. Maybe there are fanfictions where new characters are introduced into the babysitting scenario, creating more complex and engaging storylines.
One idea could be creating an OC who is a transfer student with a mysterious past related to the babysitting club. For example, the OC's family might have a connection to the school that is slowly revealed. Another idea is an OC with a unique talent, like being able to communicate with animals, which could add an interesting dynamic to the babysitting situations. A third idea could be an OC who has a different cultural background and introduces new games and traditions to the kids in the club.
One idea could be an OC who has a special talent for music and uses it to soothe the children at the babysitting club. For example, when the kids are having a hard time going to sleep, the OC plays a soft lullaby on their guitar.
Create a character arc for them. Let's say your OC starts off as really clumsy and unsure in the babysitting club. But as they interact more with the kids and the other babysitters, they grow in confidence and learn new skills. This development over the course of the fanfic will make the character memorable. You can also give them some funny or endearing catchphrases that they use often, like 'Oh my stars!' when something unexpected happens.
First, consider their appearance. It doesn't have to be overly detailed, but it should give readers an idea of what the character looks like. Then, for their personality, make it multi - faceted. A believable character isn't just all good or all bad. They might be kind but also have a short temper sometimes. In terms of their relationships, think about how they interact with the existing characters in Gakuen Babysitters. Do they get along well with the kids? Are they intimidated by the older students? Also, let their character develop over the course of the fanfiction. Maybe they start off being clumsy in babysitting but gradually improve.
From what I can assume, if it's like other similar works, it may have a unique power system. For example, characters might possess special abilities or powers that are related to their identity in the school or the world they are in. This could lead to battles or competitions among the characters, which is a common and exciting element in such stories.
I'm not very familiar with 'masou gakuen hxh' specifically. But generally, for anime similar in genre, you could check out 'Sword Art Online'. It has a similar theme of a unique school - like setting within a virtual world. Another one could be 'Log Horizon' which also involves characters in a game - like world and their adventures.