The are pious followers of the Jōdo Shinshū sect of Japanese Buddhism.
Myōkōnin, which means "a wondrous, excellent person", refers to a devout follower of Jōdo Shinshū who lives a life of total dedication to Amida, the Buddha of the Western Pure Land, and whose acts and sayings, though they may often run counter to common sense, reveal the depth of faith and true humanity.
Myōkōnin were largely unheard of in the West until D. T. Suzuki introduced them in his lectures and writings on Jōdo Shinshū. Most myōkōnin left few, if any, written records, but one of them, Saichi, is noted for his numerous poems expressing his devotion to Amida Buddha.
Myōkōnin have been documented from the Tokugawa period to modern times.
References
http://purelandnotes.com/pln_1/ag3d.htm
http://shin-westhartford.tripod.com/id18.html
http://www.dictionaryofspiritualterms.com/public/Glossaries/terms.aspx?ID=394
http://www.threewheels.co.uk/index.php?option=com_content&task=view&id=14&Itemid=9