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