Advanced gearing
Introduction
This guide will focus mainly on Britra's mechanics and the general framework for building a team to beat Britra comfortably.
Britra bosses have two different versions; Awakened (lvl 130 and 150) and non-Awakened (lvl 70, 90 and 110). Both versions have different mechanics.
Important Mechanics (Non-Awakened Britra)
The non-Awakened Britra has three important mechanics to look out for. The first is a slam attack, which is used twice at about 80% and 20% hp. This attack does a large amount of AOE damage in a single hit, and can easily wipe out important backline units. You can avoid it by either using shields or a counterattack character (like Shiyoon) to counter it.
The second mechanic is Britra’s ult, where it will start a DPS check; If you fail it, Britra will knock back all your units while doing multiple instances of damage. This attack can also easily kill backline units, so make sure to avoid it by doing enough damage.
The final mechanic is Britra’s siege mode. At slightly below 50% hp, Britra will start directly attacking your ship instead of your units. To get past this phase, you have to damage Britra until it hits 20% hp (where it will do the aforementioned slam attack) without your ship dying.
Shiyoon, Awakened Shiyoon, or Ella are highly recommended for non-awakened Britra runs, because they can counter both the slam attack and Britra’s specials.
Important Mechanics (Awakened Britra)
Awakened Britra’s primary mechanic is a universal debuff which decreases ATK and Skill Haste while also increasing damage taken on your units. However, it does not affect every unit type at the same time. For about the first minute of the fight, Britra applies those debuffs to Counters and Mechs only; for about the next minute, the debuffs are applied to Counters and Soldiers only; for the rest of the fight, the debuffs are applied to Soldiers and Mechs. As you may already be able to tell, the final phase not debuffing Counters is crucial, as it allows you to burst Britra down using Counter units.
In addition to those debuffs, Britra has universal healing reduction and barrier disruption (barriers are instantly destroyed by attacks and do not absorb any damage). These debuffs are not phase-dependent and apply to all units for the entire fight.
You also will want to avoid awakened Britra’s specials. There are two versions of it; one pushes your units away, while the other pulls your units towards Britra. It is completely random as to which version of the special is used. The pull is the more dangerous of the two, but you should still be aiming to avoid both specials as much as possible, because they will completely annihilate your team, while the universal healing reduction prevents you from properly healing any surviving units.
Since this version of Britra is awakened, only Awakened Shiyoon is able to counter the specials (making him essential to Awakened Britra runs). SR Shiyoon and Ella will not work. However, there is an element of RNG when using Awakened Shiyoon; Due to the Skill Haste debuffs that all counters will be experiencing in the first 2 minutes of the fight, he relies heavily on using his Passive Skill counterattacks to reduce his Special Skill cooldown (Passive Skill counterattacks can only counter incoming basic attacks, and will reduce Special Skill cooldown by 6 seconds), and he can only use his Passive Skill counterattacks after every 4th CRIT attack. The RNG here should be obvious enough: If he does not CRIT enough, he will not get his Special Skill in time to counter Britra's next Special Skill.
Fortunately, there is a better alternative to using Awakened Joo Shiyoon: A unit called Jin Bora. All her basic attacks will increase an enemy's skill cooldown by 1s, which allows her to permanently prevent Britra from using any skill at all.
Basic Team Building for Awakened Britra
Since team building for non-Awakened Britra is very easy, this section will focus solely on Awakened Britra.
As mentioned previously, you need to have either Awakened Shiyoon or Jin Bora in your team for Awakened Britra. Any team without either one of these two units will simply not work for reliably clearing Awakened Britra.
For frontliners, you will need to use a Soldier frontliner for the first minute of the fight, a Mech frontliner for the second minute of the fight, and a Counter frontliner for the final minute of the fight, due to the way Britra's debuffs work. Administration Shieldman is tanky enough to work as your Soldier frontliner, while the Mech robots spawned by Sigma from her Ultimate Skill are more than enough for your Mech frontliner needs (Sigma will also generate valuable Deployment Points over time for your team). For your Counter frontliners, you will want someone who can also provide utility, because the final minute of your fight is also your burst phase. There are multiple choices for this case, with Chifuyu and Awakened Chifuyu being two top options.
For your DPS, support, and buffer units, you will want to use Counters that are able to stay out of Britra's basic melee attack range. Even when Britra is targeting a frontliner, its attacks will still be able to hit some ranged units like Gaeun and Harim. A few examples of good units which are able to stay out of Britra's melee attack range are Orochi, Agnes, Sky and Awakened Maria.
As mentioned previously, the final minute of the fight is when Britra transitions to a phase that does not debuff Counters. This then allows you to use units, which would have died in earlier phases, to further strengthen your burst damage. The most prominent example of such a unit is Seo Yoon.
Videos
For reference, I have linked two videos below. The first run is based on a Jin Bora team, while the second run is an older video based on an Awakened Shiyoon team.