The Seafloor Palace
The Seafloor Palace is the seventh chapter in Kid Icarus: Uprising's story line. This Chapter features the return of the death god, Thanatos. Pit makes his way toward the Seafloor Palace in order to stop the invasion Thanatos lead, and obtain the Underworld Key.
 Air Battle
During the aerial portion, Pit must make his way to a palace, located underwater, on the seafloor. Palutena explains how Thanatos, who was known originally as Tanatos from the original Kid Icarus game, has returned and holds the Underworld Key, which is necessary to gain access to the Underworld. After making his way through some enemies, Pit reaches an ocean, which splits in half. Palutena claims it was her doing, when moments later, the god of the sea, Poseidon interferes and claims that he was responsible for splitting the ocean. This allows Pit to make his way to the Seafloor Palace without having to hold his breath. Numerous enemies are introduced as he makes his ways through the ruins at the seafloor. As Pit eventually arrives and enters the palace, Poseidon closes up the ocean, killing off the remaining enemies.
 Land Battle
During the land portion, Pit must explore the palace and find Thanatos. In the palace, consists of some ice-based enemies, who can freeze Pit if attacked. Also, the palace holds traps, such as water pits, as well as electrical obstacles. There's also a point where Pit must ride a moving platform while avoiding enemy attacks that can knock him off the edge. Throughout this Chapter, Thanatos makes pointless remarks that eventually annoys Pit and Palutena. After successfully making his way through the Palace, Pit will encounter Thanatos.
 Intensity Gates
The first Intensity Gate, which requires an intensity setting of 9.0, is located in the room where you begin the land portion. Inside the room are multiple enemies, in which Pit must defeat in order to proceed. If successful, he can access a random item from the Treasure Chest, as well as get the Drink of the Gods and Lightning of Judgment items,
The second Intensity Gate requires an intensity setting of 4.0. Inside the room consists of a few enemies and a Treasure Chest, which holds a random item.
 Boss Battle
The boss of this Chapter is the death god, Thanatos. He has the ability to shape shift into many objects and mainly attacks from a distance. During the course of the battle, he can take on up to five forms.
- Blade Form - He turns into a blade and surrounding him are multiple blades, all of which attack, when Pit gets too close.
- Bat Form - He transformers into a swarm of bats and can toss projectiles.
- Atlas Foot Form - He turns into an Atlas Foot, and attempts to stomp Pit.
- Pot Form - He appears as a giant pot, which shoots out skulls that Pit must reflect in order to deal damage.
- Doll Form - His doll form simply hops around the field. You have to attack the red spot on his body, which opens the doll, revealing a second, smaller doll. Shoot the red spot again on the second doll and an even smaller doll appears. Keep up the process until Thanatos appears.
After dealing enough damage in the majority of his forms, he will revert back to his original form, giving you the opportunity to finish him off and obtain the Underworld Key.
- This is the only Chapter with an Intensity Gate that requires you to be on an intensity of 9.0, which is the highest difficulty setting.