- "The Keeper's skull may eviscerate our enemies, but the secrets it illuminates - THAT is what concerns me."
- — Edward Richtofen upon taking the Skull of Nan Sapwe.
This weapon has two attacks. The first attack called Vaporize: it raises zombies in the air before obliterating them. While the secondary attack is called Mesmerize, it makes any aggressive zombie, Spider or Thrasher docile within the field of view of the Skull. This can also be used to reveal hidden objects and effects around the map and is required for the Seeds of Doubt.
The Skull itself is housed in a hidden altar accessed by "cleansing" the four bloody skulls found on the Trials of the Ancients altar. Each skull having a symbol on the altar side it is placed on along with being etched into the frontal lobe. One skull can be taken at a time to a cleaning pedestal to remove the blood. The cleansing pedestals are found at:
- In-front of the map spawning location.
- By the Propeller Trap, closest to the bottom most switch for it.
- In the Bunker Dock, in the center of the area.
- In the Bunker lab area, in the center of the room that has the KT-4 tables.
Placing a skull within a pedestal will set off a defend wave where zombies spawn in with a green glow around them which will go after the skull. If the skull takes too much damage in this time, it will be destroyed and return to the altar on the next wave. The first skull only having standard zombies but the second to fourth having Spiders while the third and fourth will also include Thrashers.
After each skull has been cleansed and returned to the altar, a new staircase will unlock in front of the altar itself. Inside this area is the Skull of Nan Sapwe sitting uncharged on a pedestal. Attempting to pick it up will cause the room to lock and Keepers will start to spawn, going after the skull.
Unlike the prior cleansing defenses, Keepers must be killed to charge the Skull and to end the defense. With completion re-opening the exit and allowing the Skull of Nan Sapwe to be picked up and utilized.
As the Mesmerize can be utilized to locate and activate hidden objects in the world, it is key for:
- Accessing the elevator for Seeds of Doubt.
- Upgrading the KT-4 to the Masamune.
- Locating the unique spider for the Spider Bait.
- Obtaining the Golden Bucket.
- The Ultimate Sacrifice (20 / Silver Trophy ) - In Zetsubou No Shima, retrieve the Skull of Nan Sapwe.
- Seeds of Doubt (75 / Silver Trophy ) - In Zetsubou No Shima, the one must be saved.
- Inside the area in which the Skull of Nan Sapwe can be obtained, the player can reveal secret storyline information about the Keepers using the mesmerize attack. Doing so will prevent the Skull of Nan Sapwe's ammunition from being reduced without using it.
- Through translation of the Keeper runes, it seems to tell the story of a Keeper who arrived on Pohnpei, protecting it and it's people. At some point, an evil "rose", or arrived at the island, forcing the Keeper to sacrifice himself, using his Skull to protect the island. His skull would then be sealed away.