Complete the game on normal difficultyStory-related and cannot be missed.
Self-explanatory! This trophy is for completing the game on (at least) Normal difficulty. Once you defeat the last boss(es) of the game (see Of Wulfs and Demons ), the game is over. After the final cutscenes and whatnot, the trophy will pop.
See Vampiress for some overall tips for playing the game on either difficulty level.