It's been ages since I could really enjoy a shoujo, not since the beginning of the punching Princess, but damn this is good. I do hope it doesn't into generic garbo though like that did.
I like a very "take charge", brutal kind of villainess! Hopefully someone will pick this one up. I appreciate the original fanlator for bringing this into my life, so let it not stop here😁!
It's a common mistranslation because they both make use of the same word -- 義理の妹. And doing things with just MTL, the crucial factor of the context of their relationship is lost.
It's also way easy to prove to yourself as well. Just use Google's translate tool to translate 'step sister' to Japanese. Then use the "swap languages" function and see the result.