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