A genius onmyoji and visionary who had appeared in the midst of the Great Pacific War and would be known as the father of modern Onmyoudo. It was through his actions that the art of Onmyoudo was able to revitalized itself in Japan by creating a new foundation, attaining him fame as well as many followers.

Him being a key figure in the Japanese Imperial Army and his leadership of the Onmyo Agency won the military and the country many victories.

However, he also caused the Great Spiritual Disaster which brought about the country's immediate downfall in the war. Despite the controversy that had risen toward him in the aftermath of this, his legacy is still enormously respected and revered. Little is known of what happened to him afterwards, but there are many who theorize that Yakou's grand ritual may not have necessarily failed and that he has actually undergone a reincarnation.

These theories and rumors are further fueled by divination, predicting that Yakou would incarnate himself half a century later as the next head of Tsuchimikado household. His powers would blossom and he would once again rise up and lead the Onmyouji to a new era. Many of those who are strongly devoted to him refer to Yakou as the King of North Star/Polaris King.