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