I found this new Japanese sect to be interesting. They reject the Mahayana sutras and only hold the Agama sutras (Japanese: Agon) as correct. This would make Agon Shu as the Japanese school closest to Theravada.
Agon Shu is Original Buddhism
Agon Shu is a Buddhist organization based on Agama (Agon) Sutras which Shakyamuni Buddha originally taught to his disciples.
Agon Buddhism is described as the "Original Buddhism."
The Buddhism was classified into Mahayana Buddhism and Hinayama Buddhism in the past. However, this was not proper and is now classified into Original Buddhism and Mahayana Buddhism. Agon Shu falls under this Original Buddhism.
Agon Shu was established as a Buddhist organization in 1978 by Seiyu Kiriyama. He is the spiritual leader of the organization and is referred to as Kiriyama Kancho. (Kiriyama Kancho led up a Buddhist organization called Kannon Jikeikai for 30 years or so until 1978. This Kannon Jikeikai was based on the Kannon Sutra in Mahayana Buddhism. He later founded Agon Shu.)
http://www.agon.org/us/index.html

