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