One idea could be Naruto is transported to the world of Little Witch Academia. He could attend the academy, but with his ninja skills, he'd be a very different kind of student. Maybe he'd try to use chakra instead of magic at first and create some interesting chaos.
The 'Little Witch Academia' original story follows Akko, a young girl with a big dream of becoming a witch like her idol, Shiny Chariot. It's about her adventures at Luna Nova Magical Academy. She faces various challenges in learning magic, makes friends with other witches - like Lotte and Sucy - and they all grow together while uncovering secrets of the magical world.
It's about the world of witches in an academy setting. It likely follows the adventures, studies, and friendships of young witches, much like the Little Witch Academia anime. There could be magic lessons, rivalries among students, and quests related to magic.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). There are often tags and filters that can help you narrow down to the specific crossovers between My Hero Academia and Little Witch Academia. Many authors post their creative works there, and you can find a wide variety of stories, from action - packed adventures to heart - warming friendships.
First, know the characters well from both series. Understand their personalities, powers, and backstories. This will help you create believable interactions in your fanfiction. For example, if you're writing about Izuku Midoriya from My Hero Academia meeting Akko from Little Witch Academia, you need to think about how their different outlooks on heroism or magic would play out.
The themes of friendship and believing in oneself from 'Little Witch Academia' could be further explored in the context of Kingdom Hearts. How the characters face the darkness and find the light within themselves while also dealing with the Heartless could make for a very engaging fanfic. The relationships between the 'Little Witch Academia' characters and the Kingdom Hearts regulars like Donald and Goofy could also be developed in unique ways.