Armored Core 6: How to unlock the secret Rokumonsen boss fight

FromSoftware's latest mech-action game, Armored Core 6: Fires of Rubicon, might look and feel very different from the developer's previous titles, but it still retains some key aspects of their signature game design. One such feature that makes a return from the Souls games is the inclusion of optional boss fights, which you might completely miss during your first playthrough of the game.

While the linear mission-based progression might suggest otherwise, there are plenty of instances where Armored Core 6 allows players to make certain decisions which results in them engaging in secret boss fights. One such secret boss is Rokumonsen, who can be encountered in Chapter 3.

What makes the Rokumonsen boss fight even more special is the way you unlock this boss fight. Here's a comprehensive guide on how to unlock this secret boss fight in Armored Core 6: Fires of Rubicon.

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Where to find Rokumonsen in Armored Core 6: Fires of Rubicon

It is in one of the earliest Chapter 3 missions, which involves eliminating V.VII Swinburne, that you will get the option to instead fight Rokumonsen, a Rubicon Liberation Front (RLF) AC. The mission tasks you with stealthily infiltrating Swinburne's base, which can be a daunting task, especially with the added pressure of staying away from the prying eyes of the MTs roaming in the area.

The best way to approach this mission is to stick to the corridors of the building to the right. Although there are MTs patrolling this area, they are fewer in number and scattered far apart. I found it quite easy to simply boost myself to hover midair and take down the MTs that appeared on my AC's radar. Sticking to the right side of the map also lets you avoid most of the airborne MTs as well.

Once you do make it to the end of the area, which is marked by an objective marker, you'll then need to head north, where you'll find V.VII Swinburne waiting for you. In a normal playthrough, you'll have to eliminate Swinburne, which isn't particularly challenging, even though the Tetrapod AC the boss uses is quite nimble.

However, if you take your time and listen to what Swinburne has to say, you'll get the choice to spare him, which then triggers a boss fight against Rokumonsen. Although I found this secret boss during my New Game+2 playthrough, Rokumonsen still was a fairly challenging boss fight, especially due to his high agility granted by the Firmeza AC and Bipedal legs.

It should be mentioned that, while the Rokumonsen boss fight is entirely optional, you will need to fight him if you're going for the Platinum trophy since that requires collecting all the combat logs in Armored Core 6: Fires of Rubicon.