Information:
The name of this group translates literally into "indigo monk". It comes from the name of a Blue Hearts cover band that the members were involved in in high school called "The Blue Bouzu". The simply took the "blue" and changed it to "ao". This would typically mean "blue", but the kanji they chose to write it in is actually "indigo".

The group was formed as a 3 person group in 1999, and they made their major label debut on Toy's Factory in 2004. In 2005 they would take on support member Watanabe as a full-time member.