Yami no Matsuei is a shojo manga by Matsushita Yoko (also referred to as Matsushita-sensei) and serialized in the bimonthly mangazine Hana to Yume. (Bimonthly as in twice a month and not every other month.)
The first story debuted in 1995, running in issues 7-12. This story introduced the main character Tzusuki Asato. The manga has run on and off through the last three years but has currently accumulated 11 tankobon (collections of the stories printed in the mangazine). The present story arc seems to be dealing with Hisoka's family, Hisoka getting a (some?) Shikigami, and Tsuzuki's relations with his 12 Shikigami.
The most powerful Shinigami in JuChoOh (Japan's bureau for processing the deceased) though he himself doesn't really know it. He takes care of the second block which covers mostly Kyushu. Tzusuki can summon 12 Shikigamis including Suzaku (Phoenix), SohRyu (Blue Dragon), and Byakko (White Tiger), and he generally uses Fuda magic. When he is really angry, Tsuzuki reveals another very fiercesome energy of unknown origin. He's worked as a Shinigami in the Shokan Division for the past 71 years and has gone through partners almost as fast as he goes through sweet food until Hisoka.
Tsuzuki has a rather care-free attitude (with no direction sense) but carries an enormous burden of guilt both from the work he does now and what happened before he died. When he was still alive, Tsuzuki was often persecuted because of his purple eyes. He desparately wants to be 'human' and that may be his reason for becoming a Shinigami.
He was born in the Meiji era (1866-1912). Tsuzuki had an older sister named Ruka who taught him both how to dance and how to cook. He is very good at the former but absolutely horrible at the latter (think Akane Tendo of Ranma 1/2). Tsuzuki died when he was 26 and little is known about his life but that he spent sometime in hospital as an adult, alternating between periods of insanity and sanity. Of everyone, only EnMaDaiOh and Konoe know about Tsuzuki's secrets though the Earl may know something as well.