Complex sentence: The film opens with a stunningly-drawn dream sequence of A-ko, B-ko, and C-ko--all grown up--engaged in a game of pool, which unfortunately has nothing to do with the rest of the storyline.
Split into simpler sentences: The film opens with a stunningly-drawn dream sequence of A-ko, B-ko, and C-ko engaged in a game of pool. However, this has nothing to do with the rest of the storyline.