Zwei (Treasure)
Electric 
Shotgun 
Supporter 
Burst 1 
Elysion Tier 2 Pierce Equation
■ Activates when entering Full Burst. Affects all allies.
Pierce Damage ▲ 20.13% for 1 round(s).
Pierce Damage ▲ 10.06% for 10 sec.
■ Activates when performing a normal attack during Full Burst. Affects all allies.
Pierce Damage ▲ 24.99%, stacks up to 3 time(s), for 1 round(s).
Frame Analysis
■ Activates after 5 normal attack(s). Affects all allies.
Recovers Cover's HP by 7.52%.
■ Activates when entering Full Burst. Affects all allies.
Critical Rate ▲ 18.63% for 10 sec.
■ Activates when performing a normal attack while in Pierce Attacks 101 status. Affects all allies.
Critical Rate ▲ 15% for 5 sec, stacks up to 3 time(s).
Overcharge Formula
■ Affects self.
Changes the weapon in use:
Charge Time: 1.2 sec
Damage: 50.69% of final ATK
Full Charge Damage: 300% of damage
Max Ammunition Capacity: 1
Additional Effect: Pierce
■ Affects all allies.
Pierce Attacks 101: Pierce Damage ▲ 25.03% for 10 sec.
Skill recommendations
Build
CUBES
Resilience, Pierce and Bastion are the best options to run for extra damage, but she is a pure buffer more than anything, so I would stick with faster reload times (Resilience).
OL GEAR
Basic DPS build: Max ammo capacity, Elemental DMG, and ATK. Filler lines don't matter much. Make sure you get at least one max ammo line to have an easier time refreshing her buffs.
Solo Raid Usage
This is based on the top 50 players of all NIKKE servers combined. Data is from enikk.app, check their website for a lot more raid data.
Pros & Cons
- Consistent HP cover recovery for everyone in the team every 5 normal attacks (3-ish seconds depending on team composition)
- As long as you are in full burst, her pierce buffs will refresh EVERY shot, making her a fantastic buffer for pierce (both Doros, Alice, fire Asuka...) and one-shot units (Maxwell, Snow White, Ada Wong...)
- Not worth using if you can't take advantage of the pierce buffs or in one-shot team compositions