Perhaps there's a plot where a powerful villain is using a combination of magic and ninja - like abilities to cause chaos across multiple universes. Naruto and Scarlet Witch are both chosen by some mysterious force to stop this villain. Along the way, they learn about each other's worlds and powers. Naruto teaches Scarlet Witch about chakra and she teaches him about chaos magic. They develop a friendship as they battle the villain and face various challenges together, like traversing different dimensions and dealing with the villain's minions.
A cool plot would be if Scarlet Witch accidentally creates a portal that brings Naruto and his friends into her world. Naruto has to figure out how to get back home while also helping Scarlet Witch deal with some internal struggles she has with her powers. This could involve Naruto using his ninja wisdom to guide her in controlling her magic better. The story could also have them facing off against some common enemies in Scarlet Witch's universe who are after her power and see Naruto as an obstacle.
Perhaps a fanfiction where Scarlet Witch accidentally gets transported to the Naruto world. She then uses her reality - warping powers to try and find a way back home. In the process, she meets Naruto and his friends and ends up getting involved in their battles, like against the Akatsuki. She could use her powers in creative ways, like changing the landscape to their advantage during a fight.
One idea could be that Genesis and Scarlet Witch team up to fight a powerful interdimensional threat. Their combined powers of Genesis' unique abilities and Scarlet Witch's chaos magic could create a really cool dynamic in battle.
Maybe the Scarlet Witch travels back in time to the era of Harry Potter. She could end up at Hogwarts and teach the students some new magic based on her powers. The students, especially Harry, would be fascinated by her different style of magic. They could team up to protect the school from an ancient evil that is awakened by her arrival in the past.
One idea could be that they team up to face a new, powerful magical threat that neither could handle alone. Maybe it's a dark sorcerer who is trying to take over the world by manipulating the minds of powerful heroes. They would have to combine Black Widow's combat skills and strategic thinking with Scarlet Witch's reality - warping powers.
Another aspect could be the reaction of the other Avengers or her friends. They might be overprotective or worried about how her being pregnant will impact their team dynamics.
One plot idea could be that they team up to fight a powerful magical threat that neither could handle alone. Their combined magic powers make for an exciting battle and a chance to show off their unique abilities.
A possible plot is that they both get caught in a magical trap set by an enemy. Scarlet Witch tries to break the spell using her powers but realizes she needs Black Widow's help too. Black Widow uses her quick thinking and knowledge of technology to find a way to disrupt the magic. In the process, they discover a new threat that they must then face together.
One plot idea could be that Captain America and Scarlet Witch team up to face a new, powerful villain who has the ability to manipulate time. They have to combine Captain America's combat skills and leadership with Scarlet Witch's reality - warping powers to defeat the foe.
One interesting Scarlet Witch fanfiction could be about her exploring different dimensions and using her powers in unique ways. For example, she might enter a dimension where magic works completely differently and has to adapt. Another could focus on her relationship with other Avengers in a more in - depth way, like how she copes with their different personalities. There are also fanfictions that might show her training a new generation of mutants, using her vast powers to teach them control and strategy.
There might be a Scarlet Witch OC fanfiction where the OC is from a different dimension and their encounter with Scarlet Witch causes some sort of chaos in the multiverse. The story could be full of twists as they try to fix the damage they've caused while also developing a unique relationship. It would be exciting to see how the two characters with such powerful abilities interact.