Ludmilla: Winter OwnerLimited

A Water Code Burst 3 Machine Gun main DPS used as a top-tier damage candidate in boss fights where the core stays exposed for a long time.
Debuffs and additional damage apply on normal attack and core-hit conditions, and her Burst Skill also raises Reload Speed.
You have to manage both Machine Gun overheating and hit conditions, so she takes a bit more effort.

As sustained-fire hits accumulate, enemies take increased damage taken and additional damage, and under the same condition she also gets bullet recovery. As hits on the core accumulate, more additional damage lands, and when Full Burst starts she gains Increased Critical Rate. Her Burst Skill applies Increased ATK and Increased Reload Speed at once to keep her firing tempo going.

Keep normal attack hits uninterrupted to meet the 60-hit condition.
When the core appears, lock your aim on it to also meet the Snowstorm2 additional damage condition.
Auto is enough by default; if overheating bothers you, just adjust your firing intervals by hand.

For keeping Machine Gun ammo up, prioritize the Bastion Cube, and support Reload Speed with the Resilience Cube. The Wingman Cube can add extra Max Ammo headroom. If the cube level gap is large, use the higher-level Harmony Cube first regardless of ranking.

Keep the Elemental Advantage damage and ATK lines, and stack Max Ammo lines heavily to stabilize her sustained-fire conditions. Put the one remaining line into Critical Rate to align with her Increased Critical Rate at Full Burst start.

The normal attack hit debuff and bullet recovery grow with Skill 1, the core bonus hits and Increased Critical Rate at Full Burst start with Skill 2, and the ATK and Reload Speed increases with her Burst.

Her single-target damage stands out in boss fights where the core stays up for a long time. She can't be fielded together with other main DPS candidates that use the Burst stage 3 slot, so choose between them for the same slot. She was part of a limited recruit.

An increased damage taken debuff and additional damage on enemies come together through her sustained-fire conditions.
Her Burst Skill applies a long Increased Reload Speed, keeping her Machine Gun tempo going.

Without core-hit conditions, the Snowstorm2 additional damage axis drops out.
Worrying about Machine Gun overheating can break her firing tempo.
She can't be in the same lineup as other Burst stage 3 main DPS candidates.