Delta: Ninja Thief

Water

Machine Gun

Defender

Burst 2

Elysion

Ninjutsu Acid Bomb

■ Activates when entering Full Burst. Affects all enemies.
Ninjutsu Acid Bomb: Damage Taken ▲ 12% for 15 sec.
■ Activates when using Burst Skill. Affects self.
ATK ▲ 15.04% for 10 sec.
■ Activates when using Burst Skill. Affects enemies within attack range nearest to the crosshair.
Ninjutsu Hyper Acid Bomb: Damage Taken ▲ 8% for 10 sec.

Ninjutsu Camouflage

■ Activates at the start of battle.
Effects differ according to squad formation.
Activates only the corresponding effect.
Affects self if there are no other Defender allies in the squad.
Effect 1: Creates a Shield equal to 12.25% of the caster's final Max HP for 10 sec.
Effect 2: Attract: Taunt all enemies continuously.
Affects self if there is another Defender ally in the squad.
Effect 1: Ninjutsu Camouflage: Prevents self from being the target of single-target attacks for 10 sec.
Loses effect when the caster takes damage.
Effect 2: Ninjutsu Injection: Recovers 11.22% of attack damage as HP continuously.
■ Activates when performing 200 normal attack(s). Affects self while in Attract status.
Creates a Shield equal to 12.25% of the caster's final Max HP for 10 sec.
Affects self while in Ninjutsu Injection status every 4 sec.
Ninjutsu IFAK lasts for 4 sec.
Function: Accumulates HP recovery during the activation duration, after which all allies are healed for the accumulated amount.
Effect 1: The maximum accumulated amount is equal to 155.28% of the caster's final ATK.
Effect 2: Once the duration ends, all allies are healed for the accumulated recovery amount.

Secret Technique: Ninja Overdrive

40 sec Cooldown

■ Affects all allies.
Distributed Damage ▲ 20% for 10 sec.
ATK ▲ 15% of caster's ATK for 10 sec.
■ Affects all enemies.
Deals 170% of final ATK as distributed damage.
■ Affects self while in Attract status.
Next shield's HP ▲ 20.13% for 10 sec.
■ Affects self while in Ninjutsu Injection status.
Maximum Accumulation of Ninjutsu IFAK ▲ 20.13% for 10 sec.

HP Boost Support Level Increase

■ Activates only when in combat areas. Affects Nikkes in this unit's squad.
HP support specialty skill level ▲ 1 continuously.

Skill recommendations

Skill 1

Skill 2

4-7

Burst

Build

Cube: Like all machine guns; Bastion. Unless you are super unlucky with overload stats and get no max ammunition, in that case run Resilience.

OL Gear: Simple support that doesn't have great personal damage, you can focus on max ammo capacity and anything else is filler.

Pros & Cons

Great uptime on skill 1 damage taken debuff on ememies as long as you have good rotations (15 second duration)
Pretty cheap character to build as a support on both skills and gear. You only care about max ammo capacity and any extra stats she can get, while her skills can be 7/7/4 for sustain and buffs
Not counting the restrictions on her buffs to actually work, the numbers are actually pretty good. Consistent heals, damage taken debuff and some offensive buffs if you decide to burst with her
Strong synergy on teams with Crown and Siren for great burst generation while still providing offensive buffs, shields, and consistent heals.

If there are no Defenders on the team, her shields are not that great in contrast to her heals, losing a lot of value on those team compositions
The 40 second cooldown kills a lot of possible teams to run since you are forced to run double burst 2 for her to just work, adding even more restrictions to team building with her
At the moment of her release, if you want to pair her with Defenders to take advantage of her kit, the only real options are Cinderella and Crown, both which have already great setups and alternatives, making it really hard to justify pulling or building Delta
Her taunt makes it pretty hard to keep her alive, regardless or shields or heals since it's continuous, making it almost mandatory you run her with another Defender on the team

Extra notes

If she's not paired with Crown (or overall Defender units, but not a lot of actual good picks outside Crown or Cinderella) it's not worth using her.

Her damage taken debuff is pretty good if paired with consistent heals (similar to Marciana storage, but based on her own damage), and even though her numbers are great, it's still quite niche with the current roster.

If not used on a team with another defender NIKKE, her rating would go down, considering her shields are way worse and she will taunt and, most likely, kill herself.