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