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