Here is the full list of all 34 Demonheart achievements.
Max out both Evil and Defiant points.
Max out both Good and Defiant points.
Max out both Good and Tactful points.
Read the book about demonspawn in Chapter 1.
Molest the demonspawn.
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.
Max out both Evil and Tactful points.
Finish Chapter 2.
Kill Mark.
Decipher the message in Chapter 2.
Finish Chapter 1.
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.
Kiss Ari.