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