Here is the full list of all 20 Beautiful elves achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Collect all pictures from Aki
Collect all pictures from Leiko
Assemble the first picture with Aki
Collect all pictures from Riko
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
Collect all pictures from Kohana
Assemble the first picture with Sayuri
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