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