Eunhwa

A Burst 2 Fire Sniper Nikke who gains Charge bonuses and applies a DEF reduction after her last bullet, and uses her Burst for an area debuff and ally crits.
She is rarely a main pick in story, bosses, Raids, or Arena.
Eunhwa: Tactical Upgrade is used more often in the same Burst 2 slot.

After firing her last bullet, Charge Damage and Charge Speed rise briefly, and the DEF of the enemy hit drops for a moment. Her Burst Skill deals damage and a DEF reduction to multiple enemies with high final ATK, and raises Crit Rate for all allies.

After landing the last bullet, load the buff onto two charged shots.
Use her Burst Skill when there are many enemies, timed to apply the DEF and crit buffs.
Leave her on auto by default, and only time the last bullet and Charge manually.

There is little evidence of her being paired in the same squad in the recent meta.

Two charged shots after the last bullet are her core, so set reload and ammo with the Resilience Cube and Bastion Cube. Cover sniper accuracy with the Assault Cube. If Harmony Cube levels differ a lot, use the higher-level cube before the ranking.

To make use of her last-bullet Charge bonus, prioritize Charge Speed and Charge Damage lines. Her own firepower contribution is small, so set Elemental Advantage damage and ATK as lower priorities.

Unless she is a meta core unit, save skill books and only raise Ready and Able1, Achilles' Heel2, and Turning the TideB to 4 when you use her. Her last-bullet chain and Burst debuff are the core, so level all three skills together. Maxing to 10 gives little return for the investment.

She is rarely seen in top Solo Raid lineups. Since Eunhwa: Tactical Upgrade, Emma, and Vesti lineups appeared, the base version is no longer used as a main pick.

After her last bullet, Charge Damage, Charge Speed, and a DEF reduction follow briefly.
Her Burst can apply a DEF reduction to multiple high-ATK enemies and grant allies Crit Rate.

Her Burst damage multiplier and crit buff values are low.
She needs the last-bullet condition met to get value from S1 and S2, so she takes effort.
She is rarely a main pick in the competition for Burst 2 debuff and support slots.