We've been transported to another world and given magical costumes, so I'd reckon a blood curse is not out of the ordinary here. ☆

[That, and also, blood curses are totally a thing she's done before. Probably.] But, that's right, a regular human shouldn't be able to hurt us. We can jump entire buildings in a single leap and destroy walls in one effortless punch! [yes, she tested it]

But who knows? They might not be any regular human.