Investigate BAWS Arsenal No.2 S Rank (MELEE ONLY) | ARMORED CORE VI FIRES OF RUBICON

With melee-only, this one an absolute nightmare. Each enemy can shave off a whopping 1.2k HP per shot, you have to destroy almost all of them (there's like one hidden by an skippable data log you can ignore), they're invisible, have infinity range, and to make matters worse, the later ones will jump away and teleport if you get too close. Suffice to say it takes a lot of trial and error to memorize their positions, learn how to dodge their attacks, and approach them in a way where you can melee them and they can't escape. Even if you're using ranged it can be very challenging depending on what weapons you're using. Suffice to say, you want something that with such obscenely high burst damage you can kill them before they can teleport and/or have a chance to deal damage to you.
This run was recorded after beating Balteus, beating all of the E Rank arena fighters, and getting some new parts.
NEW MELEE WEAPON: PB-033M ASHMEAD, AKA the Pilebunker. This thing hits harder than both the HI-32: BU/TTA (Emerald) and Vvc-770LB (Sapphire) swords with its charged attack. Uncharged, it is the weakest of the three, but it does good impact for staggering enemies. The Pilebunker charged attack seems to scale better with Melee Specialization compared to the others. The catch is, Pilebunker's range and tracking is terrible, especially vertical tracking. It's pretty reliable against grounded enemies uncharged, but it's borderline impossible to hit anything that moves with the charged attack. But when it works, it _works_. ASHMEAD is absolutely devastating when it connects with a charged attack, and was the only melee weapon that can one-shot the mobs in this mission. In ideal circumstances, it can hit for over 6000+ damage against staggered enemies.
NEW ARMS: EL-TA-10 FIRMEZA. Offers 10 more Melee Specialization than TOOL ARM, which translates to +5% more damage on average.
NEW HEAD: KASUAR/44Z. Only really used here for scan range, more of a sidegrade than an upgrade compared to the NACHTREIHER head.
NEW BOOSTER: AB-J-137 KIKAKU. Offers the highest melee boost in the entire game, might be what I stick with for all future melee builds.
OS TUNING: I got Melee Weapons to level 2 plus Quick Turn. Quick Turn isn't very useful in this mission, but it is for Balteus.