Here is the full list of all 34 Demonheart achievements.
Max out both Evil and Defiant points.
Max out both Evil and Tactful points.
Kiss Ari.
Ask the demonspawn as many questions as you can.
Kill Mark.
Max out both Good and Defiant points.
Read the book about demonspawn in Chapter 1.
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.
Decipher all the messages in Chapter 3.
Kiss Sir Brash.
Finish Chapter 2.
Decipher the message in Chapter 2.
Molest the demonspawn.
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.
Finish the game as Good Bright and as Evil Bright.