D

D is a Burst III SMG wielder who shines against Bosses but is pretty underwhelming everywhere else.

Her Skill 1 gives her a bit of healing during Full Burst and she will deal more damage to enemies weak to her element - since she's Wind, it will only affect Iron enemies. Also, since D's weapon of choice is SMG the healing she will get from the passive will be negligible, especially past the first trigger of the skill as then the second part of the skill won't activate.

As for her Skill 2... You know, I kinda hate the 'when the target appears' mechanic. D is the second character that uses it - the first being Viper - and honestly having a skill activate just once in the battle feels so bad.

Okay, rant over. Let's talk about what the skill actually does.

Its first part charges the burst gauge, allowing you to start your first Burst rotation much quicker on boss fights (since they are considered the 'target'). The second part of the skill gives Stun immunity to all allies for up to 36 seconds while the third part only affects D damage against Iron enemies. D is similar to Sakura as this skill is tailored to counter a specific boss - Modernia in the case of D. Not only Modernia's element is Iron, so D will deal additional damage to her, but the Stun Immunity will help a lot in that fight. On top of that, since you will be able to Burst basically right after the fight starts, destroying Modernia's Core will be much much easier.

Still, while Sakura is limited to her niche, D can actually be used against Bosses that aren't weak to her. An example is the most-hated Train - the ability to Burst right at the start of the battle allows you to destroy a lot of the parts, making this fight easier. This will make D a great choice for Union Raid too as you will be able to burst the boss down and destroy its parts much faster.

Keep in mind that this skill is useless for PVP as the target trigger condition doesn't work there - so you won't get the Burst fill or Stun immunity there.

D's Burst deals damage to all enemies which doesn't help much on bosses (even with multiple parts). The second effect of the Burst will give a significant boost to damage to all allies when fighting a boss enemy as it will help in destroying their parts faster. What's important about this buff is that the damage formula treats it as an independent multiplier, which is better than Attack (which is diluted). This means that not only D but also her Attacker allies will deal a lot more damage. The third effect offers synergy with Stun immunity - if you have it, all allies will Burst for up to 5 seconds longer which means their damage output will further improve.

Overall, while D is another niche character that you will only use on bosses, she provides the team with a new damage multiplier tied to her Burst that will make destroying boss parts much easier. This combined with the instant burst at the start of the battle in boss battles makes her a really good choice against bosses that have multiple parts that you need to destroy quickly. Sadly, in Story, you will only use her against Iron-heavy stages, and in PVP her Skill 2 doesn't work at all, making D useless there.