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