Here is the full list of all 20 Star girls achievements.
Collect all pictures from Aki
Collect all pictures from Leiko
Collect all pictures from Riko
Assemble the first picture with Aki
Assemble the first picture with Leiko
Collect all pictures from Tora
Assemble the first picture with Riko
Collect all pictures from Sayuri
Assemble the first picture with Tora
Collect all pictures from Moriko
Assemble the first picture with Sayuri
Collect all pictures from Kohana
Assemble the first picture with Moriko
Collect all pictures from Mika
Assemble the first picture with Kohana
Collect all pictures from Chizu
Assemble the first picture with Mika
Collect all pictures from Hiroko
Assemble the first picture with Hiroko
Assemble the first picture with Chizu