One of the most interesting things is how it deals with themes like regret and acceptance. The characters are all in this after - life because they have some form of unfinished business or regret from their real lives. Through their adventures in the story, they gradually come to terms with their pasts, which is a really profound aspect of the Angel Beats light novels.
One interesting concept is exploring different backstories for the characters. For example, delving deeper into Otonashi's life before he arrived in the afterlife. Another could be alternative endings, like if the characters managed to find a different way to move on from the afterlife.
Yuzuru Otonashi is really interesting. He's the protagonist who has lost his memories at first. His journey to regain his memories and find out his purpose in this afterlife is captivating. Another is Kanade Tachibana, the girl known as Angel. Her mysterious nature and her real identity that gets revealed slowly make her a very engaging character.
One interesting concept could be alternate endings. Maybe in the fan fiction, they could give a different ending to the story where all the characters get a more peaceful resolution instead of the bittersweet ending in the original. Another concept could be exploring the backstories of the minor characters more deeply. For example, the fan fiction might focus on the life of a character like TK before they arrived in the afterlife world.
One idea could be a crossover where Naruto characters end up in the afterlife world of Angel Beats. For example, Naruto and his friends could try to help the SSS members achieve their unfulfilled wishes. Another idea is to have a character from Angel Beats gain ninja powers like in Naruto. They could then use these powers to fight against the Angel in a new and unexpected way. A third idea might be a story where the concept of chakra exists in the Angel Beats world, and the characters have to learn how to control it.
One interesting Angel Beats OC fanfiction could be about an OC who has a special musical ability that changes the way battles in the afterlife are fought. For example, their music can soothe the souls of the enemies, making them question their reasons for fighting.
The main themes include the concept of second chances. These characters get a chance to do things they couldn't in their earthly lives. It's about making the most of this new - found opportunity. Also, the theme of resistance against fate. They don't want to just passively accept the rules of this afterlife world, so they fight, which shows their will to control their own destinies.
Maybe a fanfiction where Yui loses her memories and Hinata has to help her remember who she is and all the things they've been through together. He could show her the places that were important to them, like the concert stage where Yui used to perform, and slowly her memories start to come back as their relationship deepens.
Well, one interesting aspect could be the character development. The angel - like neighbor character might have a really unique personality that evolves throughout the story. Maybe she starts off as just a helpful neighbor but then her relationship with the protagonist deepens in unexpected ways.
A third idea is to create a story where the characters from Angel Beats After Story get mixed up with characters from another anime world. This would bring a whole new dynamic as they have to adjust to different rules and cultures while still holding on to their own identities and goals from the Angel Beats universe. It could be a really fun and unique fanfiction concept.
One idea could be exploring the lives of the characters in the afterlife world after achieving their initial goals. For example, they could start new projects or relationships. Another could be a time - travel twist where they go back to their past lives and try to change things. Maybe they find a new enemy or mystery to solve in the afterlife.