Each time a Survivor other than yourself is killed or sacrificed, Sole Survivor gains 1 Token, up to a maximum of 3 Tokens:

Each Token grants a stack-able radius of 20/22/24 metres within which the Killer is unable to read your Aura, up to a maximum of 60/66/72 metres.
Once you are the last Survivor standing, you benefit from the following effects:

Increases your Repair speed of Generators by +75 percent.
Increases your Opening speed of the Exit Gates and the Hatch by +50 percent.
Increases the odds of becoming the Killers initial Obsession by +100 percent.

The Killer can only be obsessed with Survivor at a time.

Prevents Crows from being alerted by your proximity and flying off, unless they are being stepped on.
Suppresses the urge to scream from any cause at all times.
Suppresses all noises related to unlocking Chests, and cleansing or blessing Totems.
Reduces their Interaction speed by 40/35/30 percent.

Increases the Action speeds of other Survivors in Healing, Sabotaging, Unhooking, Cleansing, Opening, and Unlocking by 15/20/25 percent while they are within 8 metres of your location.
This effect lingers for 15 seconds when leaving Leaders range.
Survivors can only be affected by one instance of Leader at a time.

Press the Active Ability button while running to trigger the Endurance Status Effect for 0.5 seconds.
Dead Hard causes the Exhausted Status Effect for 60/50/40 seconds.

Dead Hard cannot be used when Exhausted.