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