 In October 2007, Mitsui was placed in the unit Athena & Robikerottsu along with fellow Morning Musume member Risa Niigaki, as well as Saki Nakajima and Chisato Okai of Cute.On the November 25, 2007 episode of Haromoni@, Mitsui got the voice role of Gurossan in the anime Kirarin Revolution starring Kirari Tsukishima, voiced by Koharu Kusumi.On April 6, 2008, Hello!