Lava

“When on the battlefield, you've gotta act like it. I bet those people brought up in greenhouses have never thought about how you're supposed to aggravate or defeat the enemy. Ain't that right, Doctor?”

Lava talks and dresses like an antisocial Goth, so you might not be expecting her proactive attitude towards working with other people. At a young age, she started taking care of poor orphans in her Victorian neighborhood, and their many plights touched her deeply. Her fiery commitment to social improvement is mirrored by her Originium Arts, which allow her to conjure flames from her magical athame knife as a 3* AoE Caster.

The textbook example of an AoE Caster, Lava’s wide-range Arts attacks are perfect for burning through groups of weak enemies that would otherwise overwhelm your Operators by sheer force of numbers. Her Talent, Quick Skill Usage, gives her SP when she is deployed so she can more quickly use her Skill, Tactical Chant α, which increases her attack speed. Slow attack speed is a big weakness for AoE Casters, so this is a helpful Skill indeed.

Lava can be very useful in the early game, when Doctors may not have access to many AoE options. However, she starts to fall behind as AoE Snipers, AoE Guards, and higher-rarity AoE Casters enter the picture. Her Talent doesn’t help her to stand out (most Operators are granted Initial SP for their Skills by default) and she can’t E2-promote, so her long-term growth is limited. Even so, AoE Arts damage is such a tremendously useful tool that Lava can stay relevant for a good long while.