An interesting plot could be an OC gamer who creates a new device in the Ben 10 universe that enhances the Omnitrix's abilities. However, this attracts the attention of villains who want to steal it for their own evil purposes. The OC then has to team up with Ben and his allies to protect the device.
One idea could be Ben using his alien forms in a virtual reality gaming world. He could face off against digital versions of his enemies and have to use his unique alien abilities to progress through levels.
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.
One idea could be that the OC has a unique gamer system that allows them to level up in real - life skills. For example, they could level up their cooking skills like in a cooking - based game, and as they do, they unlock new recipes and cooking techniques. Another plot could be the OC's gamer system is glitched, and they have to figure out how to fix it while also dealing with the strange in - game - like events that are now happening in their real life.
One idea could be an OC who has a unique alien form that is a combination of two different Ben 10 aliens. This OC could struggle with controlling its powers at first. Another plot could involve the OC coming from a different dimension where the rules of the Omnitrix are different. They then have to adapt to the Ben 10 universe while also dealing with villains who want to use their unique powers for evil.
One idea could be an OC who is a gamer and discovers a hidden power within the Highschool DxD universe while playing a virtual reality game related to it. This power could be something unique like the ability to control shadows in the DxD world.
An OC who was a streamer before the apocalypse. In the 'the walking dead' world, they try to keep their spirits up by pretending they are still streaming. They document their survival journey as if they are doing a special 'real - life zombie apocalypse' stream. They might even gain a following among other survivors who find their positive attitude inspiring.
An interesting plot could be an OC gamer who is known for their role - playing skills in the human world. When they enter the Highschool DxD world, they start to role - play as a powerful being. This act fools many of the characters at first, but as time goes on, they have to actually become strong to keep up the facade and end up changing the power dynamics in the DxD world.
The gamer OC could be from our world and is somehow sucked into the RWBY world. In this new world, he realizes that his knowledge of games gives him an edge. He starts to form a harem as he helps the RWBY characters in different ways, like providing strategic advice during battles. For instance, he might suggest new ways to fight the Grimm based on his gaming experience. The relationships in the harem could develop as they train together and the OC shows his determination and kindness. Some characters might be initially skeptical of him but gradually warm up due to his positive influence.
One idea could be an OC with a unique gaming ability that allows them to level up their magic skills faster in the DxD world. For example, they could have a 'gaming HUD' that shows hidden stats of enemies, giving them an edge in battles.
You could also write a fanfiction where an OC is accidentally bonded with the Omnitrix in a way that it can't be removed. The OC then has to learn to live with it and use its powers for good, but they face challenges as they are not Ben. They might have to deal with people who are suspicious of them having the Omnitrix and also face enemies who are specifically after the device because of its new and unexpected host.