Another idea is that the OC is a time - traveler from the future who comes to Rin's time to prevent a disaster that could end the world of music. Rin, being passionate about music, teams up with the OC and they go on an adventure filled with music - themed challenges and revelations.
One idea could be a story where the OC is a new student at Rin's school. They meet during a music club event and Rin discovers the OC has a unique musical talent that she's never seen before. This could lead to them collaborating on a special musical project.
A more emotional fanfiction could be where the OC is a shy and lonely person. Rin, with her energetic and friendly nature, befriends the OC. Over time, through shared experiences like going to concerts and writing songs together, the OC comes out of their shell and they form a deep and lasting friendship.
Some Tumblr blogs focus on Love Live! fanfiction as well. You can search for relevant tags such as '#Rin Hoshizora x reader fanfiction' on Tumblr. However, the content on Tumblr can be a bit more scattered compared to dedicated fanfiction sites, but it's still worth a look.
A good 'Rin Hoshizora x reader' fanfiction often has a strong characterisation of Rin. It should capture her energetic and sometimes shy personality accurately. For example, if the story is set in the Love Live! school environment, Rin's passion for idoling should be shown in a believable way in relation to the reader.
Secondly, have a strong plot. It could be a mystery where the OC and Rin are trying to solve a music - related mystery, like a missing ancient musical score. Or it could be a love story, but don't make it too cheesy. Build up their relationship gradually through shared experiences, like competing in a music competition together.
I think it's in episode 8. But you might want to double-check as it could vary depending on different versions or releases.
A fanfiction could focus on their relationships. For example, how Sango and Miroku's relationship develops further with Kagome and Rin as witnesses. Maybe Kagome gives Sango some advice on dealing with Miroku's flirtatious nature, and Rin looks up to them as a couple, learning about love and relationships from them.
A cool idea could be a time - travel fanfic. Riki and Rin find themselves sent back in time to when the Little Busters first formed. They have to deal with the knowledge they already have while trying not to disrupt the past too much.
One idea could be that Rin, with her medical skills, tries to save Kakashi but fails due to some unforeseen circumstances. Maybe an enemy uses a powerful jutsu that she can't counter in time. This would be a tragic twist, as her being alive doesn't change the outcome for Kakashi.
One idea could be a fanfiction where Rin gets lost in a magical realm and Sesshomaru has to search for her in a world full of strange creatures and tricky magic. It would be interesting to see how he overcomes the challenges in this unfamiliar place to find her.
One idea could be that the OC is a time - traveling journalist who meets the 10th Doctor during his adventures. They initially clash because the OC is always trying to get a good story, but eventually they become friends and the OC helps the Doctor solve some mysteries. For example, in a planet where the inhabitants are losing their memories, the OC's sharp observational skills come in handy.
One idea could be that the OC is a new Bakugan brawler who enters a tournament. Shun notices the OC's unique battling style and becomes intrigued. They start to train together and develop a friendship that slowly turns into something more. For example, they might discover a new Bakugan ability while training.