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