While he has some interesting stuff going on, at the end of the day, Azrael is mostly a typical ST Arts DPS. You can pair him with your preferred Arts supports and let him loop things until they’re dead—Castoria, Urdr, and Tiamat all work about evenly well for this (albeit in different ways), and Ascalaphus and Oberon can flex in to provide additional flat NP charge and/or burst damage (though both of them cut against Azrael’s post-turn-3 damage potential and sustain tools).
Double Castoria is the most straightforward approach, of course, giving strong buffs and plenty of charge, with further damage amp from her NPs. Castoria is often the best option if you’re going to use the Castorias’ NPs to boost damage and you’re not relying on cards, or if you want to use Castoria’s defensive tools to survive to a second buff cycle.
Double Tiamat, meanwhile, lets you set up damage buffs on Azrael and then hit hard with both his NP and with crits. For this setup, you actually want your third support in the front line to start the fight. Castoria, Urdr, and Ascalaphus all work about as well here, with Ascalaphus getting a small shout-out for making Azrael more likely to land instant-kills when relevant. Whoever you pick uses their skills and battery on Azrael before plugging out for the second Tiamat. Both Tiamats use all their skills, and then you do a Tiamat/Tiamat/Azrael NP chain. Azrael can then use his battery on turn 2 to guarantee he can NP, and you can (with good card draws) use Azrael brave chains to loop and deal damage on the next two turns.
Double Urdr is perhaps the most interesting setup, as it lets Azrael double-stack all of his skills by turn 3, despite his long cooldowns. For this to work, Azrael needs Skill Reload, though he actually does not need Mana Loading. On turn 1, he uses his first and third skills, and then his second. Both Urdrs then use all of their skills, even though this “wastes” their batteries—if Azrael has Mana Loading, this gets him to 200% charge for a bit of extra damage from Overcharge, but even if not, it gives Azrael all available buffs from turn 1. Azrael NPs and refunds 20% off his NP, plus another 20% in flat charge from the Urdrs.
On turn 2, Azrael’s third skill is also back off cooldown, so you can reuse it to double the rate of defense-down scaling on the enemies. You then plug in your third support. Ascalaphus is the most reliable pick for this, as he has enough battery that he doesn’t require Azrael to draw any cards turn 1, but Oberon is also an option for amping turn 3 damage, and Castoria or Tiamat can also be good sustain-oriented picks if you’re willing to reset until you get a Quick, an Arts, or two Busters for Azrael on turn 1 to cover the extra 10% NP gauge those two need. Your plug support uses all their skills on Azrael, bringing him back to 100% charge, and he NPs again.
On turn 3, Azrael’s second skill comes back off cooldown, which he can reuse, either on himself to facilitate crits or on a support to potentially enable an NP. Reusing skill 2 in turn brings skill 1 off cooldown. Azrael can then reuse it, stacking its attack buff and (more importantly) getting its 80% battery again, guaranteeing him the loop regardless of prior card draws.
This setup gets Azrael an extra 30% Arts up, 30% Attack up, and 20% defense down on turn 3, which approximately matches the benefits of getting two Castoria NPs, without preventing you from using Azrael cards on any specific turn and while still letting you insert a Castoria NP if you really want to. On top of all that, this leaves Azrael with quite high buff value on turn 4: 110% defense down, 30% Arts up, 30% attack up, plus all the buffs from your plug support. Unfortunately, Thirst for Death doesn’t stack with itself, so it will have expired and Azrael won’t get his supereffective multiplier on turn 4… but still! That’s better post-buff-window damage than most Servants get.
As I’ve alluded to above, Azrael also has strong multicore potential. His ability to reach an NP without anyone’s help and his good in-kit steroids mean your supports can focus their attention on an AoE damage dealer, and Azrael himself has a 30% battery and 30% attack buff to offer, further mitigating the loss of a full support. Azrael will be most notable for multicore farming when an early wave has a high-HP enemy that’s susceptible to instant death: Azrael can give himself an NP to finish the enemy with an instant-kill—without needing any buffs from your main supports—and then get himself most of the way to a second NP from his own NP’s refund effect. With nearly any splashable charge—Castoria’s Charisma, for instance—Azrael can get to a second NP for turn 3, amplifying your damage against a single target while your primary AoE DPS clears the lower-health enemies.
Outside of optimized setups, Azrael works with really any Arts setup you can dream up. He’s extremely self-sufficient, bringing charge, damage, survival, and utility all on his own. Unlike many other high-battery Servants, he doesn’t even have bad cards, which means he’s not necessarily reliant on having more batteries around to NP reliably. For CQs in general, you can pair him with whatever Arts supports you happen to have handy, and he’ll do just fine. The usual Castoria stall setups are great as always—Thirty Birds in particular lets Azrael bring even more consistency and speed to a Castoria/Lady Avalon team, for example. Azrael even synergizes with Mozart’s new buff—in addition to boosting Azrael’s damage, Mozart lets Azrael NP even without Mana Loading, and his debuff success rate buff makes Azrael’s third skill much more reliable.
The Black Grail will essentially always be Azrael’s best CE, unless you’re running a drop CE for farming purposes. He his passive healing even offsets the demerit!
Azrael doesn’t necessarily need anything specific that CCs can provide. Crit damage CCs are a generically solid pick, and star gen CCs can be alright, too… but nothing CCs give will matter all that much.