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