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