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