After starting the level, there is a shop jukebox nearby, so go and buy some upgrades if you want to (or forgot to at the end of Chapter 2). Continue to make a way to the dead end to the north. There are dog enemies here, and if you kill them, you can get 60 Machine Gun Bullets. Go up the stairs and continue on the walkway until you see an item case. Drop down to get 36 Handgun Bullets.
Now head for the alley in the northwest section of this map, there's a mako point here, then approach the WRO soldier to get a cutscene. Pick up the Card Key he leaves behind and open the laser gate, then open the door to the Pub. Behind the counter, next to the stairs is the weapon the Hydra, and there's a Potion nearby too.
Continue up the stairs, there are 3 cases, which contain 36 Rifle Bullets in total. Leave through the door to the alley, there are about 4 enemies there, so take them out. Proceed forward until you reach an open area. The open area is not safe to run around in for a protracted period of time, there are several snipers lying around, so equip your Hydra and the Long Barrel and take them out one by one (they're high up, so just aim generally upwards until your gun finds a lock on someone, or you could just snipe them out, but that takes more time). There is one ground based sniper, he's hiding behind a box in the middling part of the corner to the south. The crate contains 60 Machine Gun Bullets and there is a mako point beside it.
Follow the boy into the room and kill the two soldiers within. There is a shop jukebox here also, so upgrade your weapons or replenish your items if you want, and proceed up the stairs. There are two item cases here, containing a Potion and 150 machine gun bullets. Go back to the first floor and follow the boy outside and kill the 2 soldiers that were hiding at the corner. Continue towards the lasergate and kill three soldiers after that, approach the boy to trigger a cutscene.
Follow the boy, and protect him from various enemies (a few Guard Hounds, soldiers and snipers) along the way. A good indicator for when an enemy is going to attack is to watch the boy, he will duck down and cringe slightly before enemies attack. However, this may take a few tries without getting the boy killed. One you reach the last room, kill the wait at the top of the stairs for the enemy to appear, kill him to get the card key (he seems to have more HP than other DeepGround Soldiers).
Go and unlock the lasergate to continue.
From here just follow the map and make your way to the red dot on the map. There are a huge amount of enemies here, so keep a wary eye out for them. On the way there is a Potion and 60 Machine Gun Bullets, and at the top of some stairs there is a crate containing 3000 gil. To get this, you have to shoot it, activate your Limit Break (which has higher jumping power) and jump to it. Continue onwards until you trigger a very short cutscene, so kill the first soldier after it then wait for the other two to come down to shoot them.
Continue following the map, when you reach a group of enemies behind a wire fence, before they spot and shoot at you, shoot the explosive barrels they're standing conveniently nearby to quickly dispose of them.
Restock at the jukebox shop and get ready for a boss battle.
Boss: Heavily Armoured Soldier
This boss is, as the name suggests, heavily armoured. He also has some DeepGround grunts on the ground and some snipers on the first floor walkway. It is advisable to kill off the top floor snipers first, then the ground grunts, then go the big cheese of this level. His missiles are relatively easy to dodge or shoot with your handgun, but keep away from him once he draws his sword - it deals a hefty amount of damage. It is a lot easier to kill this boss off if you have an upgraded weapon, but this isn't necessary. Shoot him with fire magic, as he's weak to the fire element to finish him off.
Eliminate the Hidden Snipers!
- There are a total of 15 snipers who are in hiding.
- The snipers in the mission does not include the ones during the boss battle, but they are annoying so kill them off during the boss battle if you want to get an 'S' rank and more gil for this mission.
Protect the Boy!
- This mission is mandatory to continue the game.