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