This is an environment that simulates cavernous habitats, primarily for nocturnal creatures. Sector 6 is a dark area in which there is always a circular light surrounding Samus. It is comprised mostly of cavern-like areas, although several futuristic styled areas are accessible. The entrance to the Restricted Laboratory is found in this sector, which is only accessible after obtaining the Wave Beam.
Samus first encounters Blue X throughout this sector, who actively seek her out to exploit the vulnerability to cold that she gained as a result of her Metroid vaccine. Once the Varia Suit is recovered, the Blue X flee from the sight of Samus not only here, but in Sector 5 (ARC) as well.
In Fusion, Samus comes here in order to obtain the Varia Suit so that she can withstand extreme temperatures, allowing her to go to Sector 5 (ARC). The second time she comes here is when she needs to defeat the Security Robot B.O.X. after it becomes infected by the X, giving her access to the Wave Beam. Despite being warned to leave Sector 6 immediately after destroying B.O.X., Samus ignores this order and enters the Restricted Laboratory that she visited the entrance of shortly before her battle with the B.O.X.
- Barrier Core-X
- Blue X
- Fake Missile Tank
- Security Robot B.O.X. (infected/second encounter)
- X Parasite
The main theme of Sector 6 is Sector 6 (NOC) Dark Area.
On Samus's first visit to this area, Facing a Huge Reaction plays during her mission briefing and continues until she leaves the Recharge Station. It resumes when Samus returns to the Navigation Room, continuing until she reaches Sector 5 after receiving her new orders.
"This sector is used to research nocturnal creatures."
"Nocturnal creatures prosper in the dark environments perfectly recreated in Sector 6."
- When Fusion is played on a Nintendo DS (including enhanced versions) or an emulator on a computer, the background is almost as bright as the spotlight around Samus. This is because these systems use a much brighter screen than the GBA.
- There are strange inactive arm-like mechanisms in the background of the nocturnal areas, that have no effect on gameplay. Similar mechanisms can be seen in the Spaceport in Metroid: Other M, the Repair Bay in Metroid Prime 3: Corruption, and throughout Area 3 in Metroid: Samus Returns. The latter is the only one of these that moves.
- The name of sector (NOC), apart of being short for "nocturnal", means "night" in Polish. It is unknown if this was intentional or not.
- Sector 6 was shown in most of the gameplay footage for Metroid Fusion in The Metroid Legacy, included in the GameCube Preview DVD.