Here is the full list of all 44 Sonicomi achievements.
Get a combo score of 100.
Get a bad ending.
Take no photos during the tutorial.
Get Ending 01.
Get Ending 02.
Get Ending 03.
Get Ending 04.
Get Ending 05.
Get Ending 06.
Get Ending 07.
Get Ending 08.
Get Ending 09.
Get Ending 10.
Get Ending 11.
Get Ending 12.
Get Ending 13.
Get Ending 14.
Get Ending 15
Get Extra Ending 01.
Get Extra Ending 02.
Get the True Ending.
Beat the game on Easy difficulty.
Beat the game on Normal difficulty.
Beat the game on Hard difficulty.
Complete 10 photo shoots.
Complete 50 photo shoots.
Complete 100 photo shoots.
Photograph a sub-target.
Go on a first date with Sonico.
Go on a second date with Sonico.
Get an SS ranking on a photo shoot.
Get a combo score of 200.
Unlock all clothing items.
Unlock all accessories.
Unlock all hairstyles.
Beat the bonus stage.
Unlock all backgrounds.
Complete all Client Requests.
Photograph 100 sub-targets.
Get all bad endings.
Get all good endings.
Buy everything in the Ouka Shop.
Reach maximum affection with Sonico.
Unlock all outfit parts.