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