Here is the full list of all 16 Sakura Cupid achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Get Mitsuki's Ending
Mitsuki's flawless plan
A friend always helps
Go back to Heaven
Find the helpless Mitsuki
It's made with love
Give in to puppy eyes
Unexpectedly effectful
Just doing a Cupid's job
Receive your punishment
"Save" Serra
Finally your aim paid off
Together in the Ferris Wheel
Get Serra into your bed
Get Serra's Ending
Achieve the Harem Ending