One interesting concept could be the unique character designs of the self - inserted original characters (OCs). They often bring fresh perspectives and abilities into the 'Kingdom Hearts' universe. For example, an OC might have a special power related to the Keyblades that we haven't seen in the original game series. Another concept could be the new storylines that are created around these OCs. They can interact with the existing characters in unexpected ways, like befriending Sora or Riku and going on adventures with them that deviate from the main game plot.
There are OCs that are popular for their strong personalities. A feisty OC who is not afraid to stand up to the villains in the 'Kingdom Hearts' universe, like Xehanort. This type of OC often has a lot of sass and courage, which makes them appealing to fans. Also, OCs that have special powers related to the heart, such as the ability to heal broken hearts or detect the presence of the Darkness in people's hearts are quite popular.
First, create a unique and well - developed original character (OC). Give them a distinct personality, backstory, and appearance. For example, if your OC is from a world not seen in the original Kingdom Hearts, explain how that world's culture and magic system influence them. Then, focus on the plot. It could involve your OC's journey to find a keyblade, or their role in a new threat to the Kingdom Hearts universe. Also, make sure to stay true to the overall tone and themes of the Kingdom Hearts series, like the power of friendship and the battle between light and dark.
In these fanfictions, the author has a lot of creative freedom. They can shape the OC to be whatever they want. The OC could be from a completely different background than the characters in the original Kingdom Hearts. This can lead to interesting plotlines. For instance, if the OC is from a world based on ancient mythology, it can introduce new enemies and challenges for Sora and the OC to face together.
In Kingdom Hearts OC fanfiction, a popular trope is the 'Mysterious Past'. The OC has a past that is slowly uncovered throughout the story, often involving a connection to a great evil or a long - lost prophecy. The 'Forbidden Love' trope also appears sometimes, where the OC falls in love with a character that they shouldn't, perhaps a Heartless or a character from an opposing side. Additionally, the 'Chosen One' trope is common, with the OC being the only one who can save the Kingdom Hearts universe from a new and greater threat.
Another interesting concept is an OC who is a member of an organization that opposes Organization XIII in a different way. Maybe they use magic that is not based on darkness or light, but something in between, which causes them to be shunned by both sides at first.
One common theme is the search for identity. Since Nobodies lack hearts initially, the OC Nobodies often struggle to figure out who they are. Another theme is redemption. They might have done things in their past as Nobodies that they now want to make up for. And of course, the theme of friendship also pops up, as they interact with other characters in the Kingdom Hearts world.
One interesting concept could be a new original character (OC) with a unique Keyblade design. For example, an OC whose Keyblade is shaped like a musical instrument, representing their love for music and how it ties into the power of the Keyblade. This could add a fresh dynamic to the battles and interactions in the Kingdom Hearts 3 universe.
One popular theme is redemption. The OC might be the catalyst for Vanitas to seek some form of redemption. Since Vanitas has a rather tragic backstory, the OC could show him a different path, a way to break free from his dark destiny.
In Kingdom Hearts fanfiction, the relationship between Vanitas and an OC (Original Character) can be really complex. It might start with conflict as Vanitas is often a rather dark and brooding character. The OC could be initially drawn into his world by accident or perhaps be a part of some grander scheme. For example, the OC might have a special power that Vanitas wants to either use or destroy.