Signal

A Fire Code Burst 2 Submachine Gun whose role is a weak debuff every 60 normal attacks, a Burst DEF reduction, and survival healing during Full Burst.
She's rarely a main pick in Story, bosses, Raids, or Arena.
She's almost never seen in top Solo Raid lineups either.

Every 60 normal-attack hits, the target's DEF and ATK drop briefly. When Full Burst starts, healing proportional to attack damage runs for a set time. Her Burst Skill damages enemies within range and applies a DEF reduction.

Keep firing normal attacks to cycle her debuff every 60 hits.
When Full Burst starts, her healing kicks in.
Leave her on auto by default and keep her hits landing at close range.

There's little evidence in the recent meta for pairing her in the same squad.

Supplement Hit Rate with the Assault Cube, and keep sustained fire going with the Resilience Cube and Bastion Cube for reload and ammo. If Harmony Cube levels differ greatly, use the higher-level cube over the ranking.

Her firepower contribution is small, so just match Elemental Advantage damage and ATK, and use the remaining lines on Hit Rate to support close-range accuracy.

If she isn't a meta main, save your skill manuals and only raise Emergency SignalB and her debuff skill to 4 when you use her. Attack Signal1 has a 60-shot condition, so its priority is low.

A low-performance debuff Nikke. Her S1 condition of 60 shots is long, so her debuff contribution is low, and her firepower doesn't meet meta standards either.

Every Full Burst, healing proportional to attack damage boosts survival.
Her Burst cooldown is a short 20 seconds.

Attack Signal1 needs 60 normal attacks, so her debuff applies late.
Her debuff values and Burst damage are low, so she's outclassed by meta debuff and firepower Nikkes.
As a Submachine Gun, her accuracy and firepower drop against distant enemies.