Complex sentence: Sayaka is an extremely spoiled daughter of one of Japan's richest families, she has never failed to dominate any sport she's cared to try, and when Yawara shows her up, she decides to stop at nothing to defeat her and becomes her rival.
Split into simpler sentences: Sayaka is an extremely spoiled daughter of one of Japan's richest families. When Yawara shows her up, she decides to stop at nothing to defeat her and becomes her rival.