One possible plot could be a Dragonborn OC who arrives in the RWBY world unexpectedly. This OC could have unique dragon powers that both attract and frighten the RWBY characters. They might initially be seen as a threat but then prove to be an ally in the fight against Grimm, using their dragon breath and enhanced strength to turn the tide in battles.
The plot could involve the Dragonborn OC having a connection to the Grimm. Maybe they are on a quest to find out why there are similarities between the dragons in their own world and the Grimm in RWBY. Along the way, they team up with Ruby and the gang, teaching them some of their dragon - based combat techniques, like using their scales as a form of armor.
A Dragonborn OC can fit into the RWBY universe by having their own unique backstory related to dragons. For example, they could have been born in a world where dragons were both feared and revered. When they enter the RWBY universe, their dragon - like abilities such as enhanced speed, strength, and the ability to breathe fire or ice can make them stand out. They could become a new type of huntsman or huntress, using their powers for good.
A really cool plot idea could be that the OC Dragonborn has a split personality. One side is a fearless warrior, ready to take on any dragon or foe. The other side is a pacifist who tries to find non - violent solutions to problems. This internal struggle could be a major part of the fanfiction, as they deal with the challenges of being the Dragonborn in Skyrim and having these two conflicting natures.
One interesting concept could be the combination of the unique abilities in RWBY, like semblances, with the powers of a Dragonborn. For example, a character might use their Dragonborn shouts in combat along with their RWBY - style weaponry. Another concept could be the cultural clash between the worlds of RWBY and the Dragonborn's realm. How would the RWBY characters react to the ancient Nordic - like cultures associated with the Dragonborn? Also, the idea of a character being both a Huntsman/Huntress and a Dragonborn, having to balance the two very different sets of responsibilities and powers, is quite fascinating.
A good plot could start with the discovery of the necromancer OC. Maybe the RWBY team stumbles upon them in an old, haunted place. Then, there could be a mystery around the OC's powers. Are they a threat or an ally? As the story progresses, an ancient evil that the necromancer once tried to stop could be resurfacing. And the OC has to convince the RWBY team to help them stop it. Another idea is to have a plot where the necromancer's past actions start causing problems in the present. For example, something they brought back from the dead is now out of control and they need to fix it with the help of the RWBY gang.
A unique plot could be the Dragonborn training the RWBY characters in the ways of the Thu'um (the Dragon shouts). Imagine Ruby and her team learning to use shouts like 'Fus - Ro - Dah' to enhance their combat abilities against the Grimm. It would be a great way to blend the two universes' combat elements.
Maybe the OC is a Grimm researcher who is specifically interested in Dragon Grimm. They go on an expedition to find a rare type of Dragon Grimm. Along the way, they encounter a group of Huntsmen and Huntresses who initially suspect the OC of being a threat. But as they face challenges together, they start to trust each other. The OC's knowledge about Dragon Grimm helps them all survive various attacks from other Grimm.
One idea could be an OC who is a Hitman but has a change of heart after encountering the RWBY characters. Maybe they start to see the value in protecting the innocent rather than just taking contracts.
Perhaps the OC's Gamer system is glitched in a way that makes them perceive certain Grimm as video game bosses with specific attack patterns. They have to figure out these patterns to defeat the Grimm more effectively, adding an interesting twist to the battles in RWBY.
Another plot could involve the OC reincarnating into an existing character's body. This would lead to a lot of internal conflict as they try to adjust to the new identity while still having memories of their past self. They could also use their new position to change the course of events in the RWBY universe.
Maybe the OC has a special power that only Penny can understand or help control. For example, if the OC can manipulate time in small bursts, Penny's robotic nature might be able to analyze it and they could use this power to save the day during a Grimm attack.