YOU SAID:
You're just somebody that I used to know
INTO JAPANESE
あなたは私が知っていたただの誰かです
BACK INTO ENGLISH
You are just someone I knew
INTO JAPANESE
あなたは私が知っていたただの人です
BACK INTO ENGLISH
You are just the person I knew
INTO JAPANESE
あなたは私が知っていた人です
BACK INTO ENGLISH
You are the one I knew
INTO JAPANESE
あなたは私が知っていた人です
BACK INTO ENGLISH
You are the one I knew
That didn't even make that much sense in English.