Juurokusai (十六歳; Sixteen) is Sayashi Riho's fourth solo photobook. It was released on March 25, 2015 including a making-of DVD.
"Debuting at the age of 12 and currently being a high school student, she has grown enough to play a central role in the group after the graduation of Michishige Sayumi. This work shows shots from two different locations; photos from Okinawan midsummer as well as the deep snow from Ueda, Shinshu. Innocence and full commitment are not the only things that can be seen; please pay attention to the different facial expressions."
- A release event for this photobook was held on March 30, 2015.
- The matching DVD release to this photobook is Sayashi Riho's 6th solo image DVD Sixteen.
- Juurokusai has been released 1 year and 4 months after Sayashi Riho's previous photobook, Taiyou, breaking the streak of her releasing a photobook every year (2014 being the year without a physical photobook release).