Elegg

An Electric Burst 2 Machine Gun Supporter.
She grants increased distributed damage and reduces the marked target's DEF, and her enemy projectile interception support lasts the whole battle.
She needs to meet hit-count conditions and BOOM InstallB marks at the same time, so she takes some effort.

At battle start, all allies gain a lasting damage increase against enemy projectiles they attack. Using Full Burst grants all allies increased distributed damage, and the enemy nearest the crosshair takes Burst Skill damage plus a BOOM InstallB mark that reduces DEF. When normal-attack hits on the marked enemy meet one threshold, all allies briefly gain Increased ATK; meeting the other threshold deals additional distributed damage to the marked target and two nearby enemies. When a target first appears, she fills Burst Gauge for all allies once.

When overheat fills, transition into a reload to keep the normal-attack hit-count condition going.
Auto works by default; to stack conditions faster, just time reloads manually.
Right after Full Burst, prioritize hitting the marked target, and line up the one-time effect that fills Burst Gauge when a target appears with the early waves.

Reload and charge cover the gaps between overheats, and ammo refill cycles the hit-count condition faster. If Harmony Cube levels differ greatly, use the higher-level cube before the ranking.

Even as distributed-damage support, she's a Machine Gun, so balance ammo and Hit Rate for the hit-count condition.

Burst and Fast Charge2 handle the distributed damage increase, Increased ATK, and gauge refill, so raise Burst and the second active first, then Short Circuit1.

In boss fights with a distributed damage DPS, her buffs and mark debuff both show their value. In special interception battles with many enemy projectiles, her interception support stands out.

Grants all allies increased distributed damage and reduces the marked target's DEF in one go.
Allies' damage support against enemy projectiles lasts the whole battle.
When a target appears, she fills Burst Gauge for all allies once.

Her normal-attack hit-count support only works while you keep hitting the marked enemy.
She fills Burst Gauge only once per battle, and it isn't replenished the same way afterward.