Complex sentence: Koremasa was the son of Wada Koresuke and directly supported the Ashikaga Shogunate by the time at which he was of eligible age, becoming a primary supporter to Ashikaga Yoshiaki following the murder of Yoshiteru in 1565.
Split into simpler sentences: Koremasa was the son of Wada Koresuke and directly supported the Ashikaga Shogunate. He became a primary retainer to Ashikaga Yoshiaki following the murder of Yoshiteru in 1565.