Brief description
The Animus is a kind of VR simulator that allows for travelling in the virtual environment of someone's memories, based on their genetic code/genetic memory (it's not "actual" time travel). This means that most of the story and action in AC IV is in a (diegetic) virtual environment. The user of an Animus can interact with the environment, but if they don't follow the memories of their ancestor it might force a desynchronization. Continued use of an Animus can also result in psychological instability.