So what I'm getting from the plot so far the protagonist is in search of her missing family. People with those red tattoos are descended from same famiky with abilities. Students with elemental abilities come from separate lineage.
I get the feeling the guys not her biological brother because shouldn't he have the tattoo too
why does he call her noona in the flashback but she calls him sunbae currently? did he skip a grade or did she flunk or something? also why would they clarify that the four building managers aren’t related and then make him her long lost brother???