Otona ni Narutte Muzukashii!!! (オトナになるって難しい; Becoming an Adult is Difficult!!!) is the 4th and last indie single by S/mileage. The single was released on March 14, 2010. The Single V was released in April 3, 2010. It was also the ending theme to the anime Hime Chen! Otogi Chikku Idol Lilpri, which Maeda Yuuka, Wada Ayaka, and Fukuda Kanon voiced characters in.