OSSAN was a Johnny's Entertainment Junior group from Kansai.
- The group was put together by Yokoyama Yu of Kanjani8.
- Their name is, like most names from Johnny's Entertainment these days, made up by the first letter of their name.
- The original thought was that they'd be a group of five members.
- At the Kansai Jr. concert 2007 they started playing instruments. Everyone with the exception for Satake Koki were inexperienced by then.
- In spring of 2008, Nagao Hiroki quit the group. Later, Adachi Tasuku joined as a member and the group's name changed from OSSaN to OSSAN.
- In December of 2008, Satake Koki decided to quit the agency, which caused the break up of the band.