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