Claudia Grindelwald is the polar opposite of Sirius Black
One of them is in Slytherin and the other is in Gryffindor.
One is the perfect heir to the Grindelwald family and the other is the rebel of the Black family.
Claudia has an excellent talent for black magic and loves it; Sirius hates black magic and regards it as an evil and disgusting thing
But with the unremitting efforts of their mutual friend James Potter, they noticed how similar they were