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