One great Monsters vs Aliens OC fanfiction is 'The Newcomer in Monstropolis'. It features an original character who has unique abilities and gets involved in the adventures of the known monsters. It has an interesting plot that shows how the OC interacts with the existing characters like Susan and B.O.B.
Power and its consequences is also a theme. The OC may have some special power, and the fanfiction explores what they do with it. They could use it for good, like helping the monsters protect the Earth, or it could lead them astray if they misuse it. This theme adds depth to the story and the character of the OC.
A scary story might involve a particular monster in Monsters vs Aliens. For example, the Insectosaurus. When she gets out of control and starts rampaging through the city. Her huge size and the destruction she can cause is quite scary. Imagine a giant bug-like creature smashing through skyscrapers and chasing people.
Perhaps the OC is initially distrusted by Susan and the other characters. But as the story progresses, through various adventures and challenges, like facing a powerful alien invader, the OC proves their worth and they form a strong bond with Susan. They might have to combine their unique skills, Susan's size - changing ability and the OC's special weapon or power, to defeat the enemy.
In a fanfiction, the aliens could capture Naruto and try to study his unique abilities. The monsters then decide to rescue him because they realize his powers could be the key to defeating the aliens once and for all. The story could involve a lot of action as the monsters infiltrate the alien base to save Naruto.
The relationship might start with curiosity. The OC could be curious about Susan's abilities and Susan could be interested in the OC's origin. As they start to communicate and work together on small tasks, like helping the monsters train for a potential threat, their relationship gradually deepens.
One plot idea could be that aliens invade the Naruto world seeking a powerful energy source, which is actually the chakra. The Naruto monsters then team up to defend their world. Another could be a group of Naruto monsters getting accidentally transported to an alien planet and having to fight their way back home. They could learn new techniques from the aliens they encounter during their journey.
The plot involves a group of monsters coming together to fight against aliens. Susan becomes Ginormica and teams up with the likes of B.O.B, Dr. Cockroach, and The Missing Link to save the world from the alien threat.
One idea could be a story where the monsters and aliens have to team up against an even greater threat from another dimension. Maybe a powerful interdimensional being that wants to conquer both Earth and the alien planets.
In Naruto Monsters vs Aliens fanfiction, it's hard to say who would win. Naruto's monsters have unique ninja abilities like chakra control and powerful jutsus. However, aliens might have advanced technology and strange powers. If the aliens' technology can disrupt chakra, they could have an advantage. But Naruto monsters are used to fighting in their own world's crazy battles.
Well, there's 'The Male OC and His Monster Girlfriends'. In this fanfiction, the male OC is a scientist who accidentally creates a portal to a world full of female monsters. He then forms relationships with some of them. Another one is 'Journey with Female Monsters' where the male OC is on a quest and is joined by female monsters. They face many challenges together and their relationships evolve. 'In the Realm of Female Monsters' is a story that delves into the male OC's experiences in a realm dominated by female monsters and how he copes with the different personalities and powers of these monsters.