Sector 4 (AQA)

Overview

Sector 4, ID code AQA, is an area from the BSL Research Station from Metroid Fusion. It's dedicated to the research of aquatic environments with fish tanks and a giant coral reef. By the time Samus arrives, the sector has taken heavy damage due to a creature infected by the X called Serris capable of hyper speed. It wastes no time causing enough damage to flood most of the area. All this is made worse by exposed wires that electrify the water.

Layout

AQA is one of the larger sectors of the BSL. The upper section is home to numerous tanks, pumps, and filtration systems that keep the area running. It's also home to breeding tanks that the X waste no time taking over. Due to the damage caused by Serris, most of this area is flooded until Samus can access the pump room and drain the water. In order to get there, she has to defeat Serris first and regain the Speed Booster power up. For the most part, this area is easy to navigate without the use of suit upgrades.
 

The return trip to Sector 4 spends most of its time in the lower area. This part is a functioning reef in deep water that is impossible to navigate without the help of the Gravity Suit. X Parasites take on the form of creatures with durable shells that are impossible to crack without the help of missiles or charge shots. One such enemy is reminiscent of Draygon from Super Metroid.

Secret Message

There's a hidden conversation with Adam and a mysterious third party if the player can reach the AQA Navigation Room after defeating Nightmare without downloading the Diffusion Missiles upgrade. It requires releasing the level 4 security lock (red hatches) and then using the Shinespark to carry a speed booster charge back up to the room with the bridge to Sector 5. Once there it's a matter of traveling back to the Navigation Room to speak with a very surprised Adam.