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