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