If you like to deepen your knowledge about Reiki or simply would like to know something, before you book a session or a training course, then i highly recommend the books from Frank Arjava Petter, worlds most aknowledged reiki teacher and investigator.
Though some of his earlier books are still about Western reiki (often called: Usui reiki), the more recent ones include all of his latest discoveries of traditional reiki. All interesting and recomendable.
From Jikiden Reiki president Tadao Yamaguchi you can read about his family and the direct information, he received from his late mother Chiyoko Yamaguchi, discipula of Dr. Hayashi.
Frank Arjava Petter