Chapter 13 of Girls' Frontline picks up in the aftermath of the 'recent' Polarized Light Event, and serves as the direct conclusion to the story from that event.
For those feeling a little lost by the Lore and plot twists and turns present here, Ferrari has helpfully created some guides to understanding the new lore.
For those who have understandably forgotten some details of the story from Polarized Light, this archive can be used to review story events, although the translations are not official. Unfortunately we are currently lacking a good official way to review the story, although youtube may be able to help. Ferrari has also made an in depth explanation of some of the lore references, which you can find below.
Chapter 13 mixes mechanics challenges and combat challenges, although it lacks most of the frustration-inducing mechanics of Chapter 11. With that said, this event expected you to possess high-end Combat Echelons to S-Rank and clear them. 3* or Higher Fairies, and well-built Echelons are a must.
To clear Chapter 13, players should have at least two Combat Echelons, one AR/SMG and one RF/HG. For a smoother experience, a third Combat Echelon is recommended, however, and the guides will use three at certain points.
Further, Commanders will need to field multiple HOCs, and the guides expect them to be leveled to at least 60 with appropriate Chips.
Finally: MICA recommended 3-Star Fairies on your Echelons to clear Chapter 12. This is for a reason.
Chapter 13 also brings a new and 'exciting' farming option, 13-4, although the requirements go up significantly.
For the absolute cheapest farm, 1x Linked Level 90, SL10 Vector is needed, although there is nothing besides cost preventing you from using a 5x Linked Vector, or Micro-Uzi Mod 2+ instead.
Fairy wise, you'll need to bring at 5* Fairy with a large Damage Aura such as Artillery, or sacrifice corpse spots for tile buffs to compensate. The route is identical to the S-Rank clear, so consult that guide for the route.
Chapter 13 Unique Drop
Chapter 13's Limited Drop is Defender, a pinnacle DPS Shotgun. Defender makes no effort to be defensive, sacrificing her Armor for a massive spike Damage Skill. While a niche pick, in the right situation and Echelon Defender can perform well. She will receive a Special Equip, 20ga Slug ammo from login rewards in the near future, which gives her periodic attacks with Sure-Hit.
As usual, Defender can be farmed from 13-6 and 13-4E.