Nagasaki damsel lives in rocks and coral reefs, 5 m to 30 m sea depth. It has a dull black body in its younger years. It is bright blue with a black spot on the back of its dorsal fin.

A male is highly territorial and often fight with other males over territory.  However, when it is young it has a different color so it does not get attacked even if it enters a territory that belongs to another male.