YOU SAID:
You gotta buy her a rose.
INTO JAPANESE
あなたは彼女のバラを買わなければならない。
BACK INTO ENGLISH
You must buy her a rose.
INTO JAPANESE
あなたは彼女のバラを買わなければなりません。
BACK INTO ENGLISH
You must buy her a rose.
That didn't even make that much sense in English.