Here is the full list of all 25 Seduce Me the Otome achievements. It takes around 1-2 hours to unlock all of the achievements on Windows.
Witness Simon's Transformation with Diana and someone special...
Share some Cake with Matthew.
Give Damien his Humanity.
Accept Sam for the Man he is.
Get Proposed to by James.
Turn down sex, but keep your true love.
Unlock the Second Set of Bloopers!
Fight Malix Yourself.
Find Harold Anderson's Magic Books.
Unlock the First Set of Bloopers!
Dodge Malix in time.
Impress the House Party Guests.
Prologue Completed!
Rename the Main Character.
Preview the start of Seduce Me 2: The Demon War!
Kiss Erik under the Moonlight.
Be Eaten Alive by Diana's Pit Beast.
Prove Your Love to Suzu.
Go To Paris with Naomi.
Get Proposed to by Andrew.
Obtain True Freedom.
Obtain True Power.
Be Baptized by Angels.
Start your Adventure with Diana.
Get Shot in the head by Malix.