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