A plot could be that the adopted daughter gets into trouble at school, like being bullied. Annie then steps in to deal with the situation. She might teach the daughter how to stand up for herself in a positive way, and also have a talk with the school authorities to ensure the bullying stops.
Another aspect could be that the adopted daughter has some insecurities about being adopted. The fanfic could then revolve around how Annie helps her overcome these feelings. Annie might tell her stories of other adopted children who have grown up to be amazing individuals, and how being adopted is just another way of finding a family that truly loves you.
One idea could be that Naruto is adopted by a powerful but reclusive shinobi. This shinobi could teach Naruto unique and forbidden jutsu, which would set him on a different path in his ninja journey. Another plot could involve Naruto being adopted by a family outside of the Hidden Leaf Village, and he has to learn to adapt to a completely different ninja culture. He could also bring some of the Leaf Village's values to this new place and cause a stir.
A simple plot could be that Ruby is a foreign ninja who comes to the Leaf Village seeking asylum. She has a special ability to control plants, which is unheard of in the Naruto world. The Leaf Village ninja are initially suspicious of her but as they get to know her, they realize she can be an asset. Together with Naruto, they face off against an enemy who is using dark magic to wither all the plants in the land, and Ruby's powers are crucial in reversing this.
One plot idea could be the adopted daughter discovers she has a unique power. Maybe she can communicate with animals like Batman can with bats. This new power causes some chaos as she tries to figure it out and also keep it a secret from Batman at first. Another idea is that she gets into trouble at school because of her association with Batman. Bullies target her, but she uses her martial arts training (that Batman taught her) to defend herself in a really cool way.
One idea is that they are time - travelers. They accidentally get sent back to the 1960s and have to figure out how to get back while also getting involved in the local music scene of that era. Maybe they meet some famous musicians from that time and learn new musical styles.
One plot idea could be that the adopted Barry Allen discovers he has a unique connection to a parallel universe where his birth family resides. He then embarks on a journey to find out more about his origins while still maintaining his relationships in his adopted family. Another could be that he uses his speed - force powers in a creative way to solve problems within his adopted family, like preventing a family member from making a big mistake in time. A third idea is that an enemy targets him specifically because of his adopted status, thinking it makes him vulnerable, but Barry proves them wrong.
One idea could be a time - travel fanfic where Danny's daughter travels back in time and meets a younger version of Danny. This could lead to some interesting interactions as she gets to see a different side of her father and also has to navigate the past without changing the future too much.
A plot could involve a group of rogue ninjas who find a way to summon an Altera - like entity. This entity starts causing chaos in the ninja world by disrupting the natural flow of chakra. The main characters then have to find a way to stop it, which might involve learning about ancient sealing techniques that were once used to deal with similar threats. It could also lead to the discovery of a hidden connection between the Naruto world and the realm from which Alteras originate.
A possible plot is that the daughter is sent on a quest to find a lost artifact that is crucial for the balance of the ocean. Along the way, she discovers secrets about her family's past that her father has been hiding from her. This could lead to some tension between them, but also help her grow as a character. She could also face challenges from other Atlantean factions who don't believe she is worthy of this task because she is still young and inexperienced.
A fanfic could be written about Abed and Annie going on a road trip together. Along the way, they discover new things about each other, and perhaps encounter some of their old classmates in unexpected places. It could be a story of self - discovery and the deepening of their friendship, with the potential for it to turn into something more romantic.