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