Complex sentence: Following his duty as a member of the Asakura family, Yohken entered the Shaman Fight of 500 years ago to defeat Hao Asakura, which he did, with the help of Matamune, Hao's former companion.
Split into simpler sentences: Following his duty as a member of the Asakura family, Yohken entered the Shaman Fight of 500 years ago to defeat Hao Asakura. He successfully accomplished with task with the help of Matamune, Hao's former companion.