Complex sentence: After his sister is captured in the attack, Ryu sets off to rescue her; in the process, he becomes involved a race to uncover seven mystic keys, which the Dark Dragons intend to use to free a goddess of destruction.
Split into simpler sentences: After his sister is captured in the attack, Ryu sets off to rescue her. In the process, he joins a race to uncover seven mystical keys, before the Dark Dragons can use them to unlock a goddess of destruction.