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