For more info, please join the server and read the lore. This part is far too hard to explain, so here's a very brief summary of it:
Every lore/story ever told(Anime,manga,show,movie,your own original ideas,etc) all happen in their own Universe/Multiverse.
What connects them all together is that they exist within what we call the 5th Dimension.
Your character is the most powerful(or among the most powerful) beings in their own native lore (Universe/Multiverse).
One day, some masked stranger comes out of nowhere, kidnaps your character and wisks them away to the illusive 6th Dimension, which no one ever even heard about before.
There, your character is turned back into a 16 year old where they are forced to attend an school to become even more powerful. No explanations given, but failure means death, and the only way to escape is to graduate, or answer a series of answers on a magic stone tablet (but a single wrong answer kills the one who wrote it). And all teachers are stronger too!