YOU SAID:
He cannot be the nicest person ever.
INTO JAPANESE
彼は今までで一番素敵な人にはなれない。
BACK INTO ENGLISH
He can't be the nicest person I've ever been.
INTO JAPANESE
彼は私が今まで行った中で最も素敵な人にはなれない。
BACK INTO ENGLISH
He can't be the nicest person I've ever been to.
INTO JAPANESE
彼は私が今まで行った中で最も素敵な人にはなれない。
BACK INTO ENGLISH
He can't be the nicest person I've ever been to.
That didn't even make that much sense in English.