SSJ4_Sayu
Both Nathan and Shizu knew they weren't human, that much was given, considering the stuff they can do. The only one who knew what they really were, were their mother, as their father sadly passed away a few years after they were born, and she intends to keep it that way, for as long as she can, anything to keep them son safe and protected.
However, when her son stopped a threat when he was 12, she knew that the peaceful life she had planned for them is thrown out the window. While trying to find a way to help her kids, she gets a call from an old friend of hers, telling her about an academy on a faraway island, as the island itself has a massive city in it, where her children would fit right in with the students attending the academy.
And now, with basically no other choice since their mom demanded it, the twins set off towards an adventure on the island, in the city, as they explore the academy and feels excited to see all these other people with supernatural abilities. Except, there's one thing that bothers Nathan, he wishes he didn't have to study or do things like homework.