Detonator with solid 1x1 scaling.

S

+Unique chain combo grants her the best unbuffed chain damage for bossing in the game after Azure, while also granting her reasonably decent mob clearing.

+One of the few good global AoE actives that doesn't require heavy breakthrough investment; possibly the best mobber in the game

-Sniper style active weakens overall bossing DPR

The fact that Requiem can save Vis for increased damage is…interesting, but ultimately gives her an active DPR of 112.5%. Very good relative to other snipers, and it gives her monstrous mob clearing potential, but it's still not enough to make her the best in slot against multi-tile bosses. She's therefore way more reliant on her chain combo to handle bossing, which, while very good, is still outdone by dedicated Detonators. Fortunately, the "hardest" stages in the game (Spire 90+, Codex, etc.) are actually pretty focused on this hybrid of mobbing and bossing, so the trade-off compared to something more straightforward like Michael is actually pretty relevant. A great example is F96, where Requiem can completely delete Wave 4 in a single active and save a ton of precious turns. While her quirks ultimately hold her out of SS tier, it would be foolish to think she's anything short of busted in the stages you want her.