Here is the full list of all 34 Demonheart achievements.
Max out both Good and Defiant points.
Finish the game as Good Bright and as Evil Bright.
Max out both Evil and Tactful points.
Max out both Evil and Defiant points.
Kiss Ari.
Kill Mark.
Finish Chapter 5.
Decipher the whole message in Chapter 5.
Molest the demonspawn.
Finish Chapter 4.
Read all the entries of Rivera's journal.
Decipher the message in Chapter 4.
Finish Chapter 3.
Ask the demonspawn as many questions as you can.
Decipher all the messages in Chapter 3.
Kiss Sir Brash.
Finish Chapter 2.
Decipher the message in Chapter 2.
Max out both Good and Tactful points.
Finish Chapter 1.
Decipher all the messages in Chapter 1.
Examine Mr. Edgardo after the dinner with Orchid.
Read the book about demonspawn in Chapter 1.