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