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