Leona

A Water Code Burst 2 support Shotgun who applies crit, Hit Rate, and pellet support all at once in lineups with two or more Shotgun DPS.
When her Full Burst start buff and max Roar stacks line up, she greatly raises the ceiling of a Shotgun main DPS.
In squads with few Shotguns, her contribution is lower than others in the same slot.

As normal attacks accumulate, Roar's Increased Critical Rate stacks multiple times on all allies, and with further stacks, Shotgun allies gain increased Maximum Effective Range. When Full Burst Time starts, all allies gain Increased Hit Rate, and the two Shotgun allies with the highest final ATK gain increased pellets. Using her Burst Skill gives all allies Increased Critical Damage, and if she is at max Roar stacks, all Shotgun allies also gain Increased Critical Rate.

Keep normal attacks going without interruption to max out Roar stacks, then use her Burst Skill in the same Full Burst.
Increased Hit Rate and increased pellets apply when Full Burst starts, so arrange the Burst order so your Shotgun main DPS fires right in that window.
On Auto, Roar stacks build by default, but if you're worried the stacks will drop right before Burst, adjust the firing interval by hand.

The Tempering Cube secures survival leeway in close-range fights through damage taken reduction. The Vigor Cube adds to the same with max HP. The Bastion Cube matches ammo refills to her own Shotgun fire. If the cube level gap is large, use the higher-level Harmony Cube first over the theoretical ranking.

Set Elemental Advantage damage and ATK as a baseline. Use Max Ammo and Critical Rate for per-shot Shotgun hit stability, and put the remaining line into Critical Damage to align with her Burst Skill's Increased Critical Damage.

Increased Hit Rate and increased pellets at Full Burst start are on Skill 2, so raise Skill 2 first. Roar stack values follow Skill 1's level. Increased Critical Damage and Increased Critical Rate for Shotguns after max Roar stacks are on her Burst, so finish by maxing her Burst.

She goes into Shotgun-centered lineups as a Burst 2 buff slot. Her value is clear when used with a Shotgun main DPS in Mirror Container and long single-boss fights. In Arena, securing Shotgun engagement range is hard, so reaching her ceiling is tricky.

Once Roar stacks are full, her Burst Skill can apply Increased Critical Damage to all allies and Increased Critical Rate for Shotguns side by side in the same window.
At the start of Full Burst she applies Increased Hit Rate and increased pellets, helping Shotgun DPS meet their conditions.

Increased pellets only applies to the two Shotgun allies with the highest final ATK.
She has no effect that reduces Burst Cooldown.
With few Shotgun allies, the support from a single Burst shrinks.

She is included in the standard recruit pool.