Ritsuka: Adam, can I ask you something?
Adam: sure, kid. What's on your mind?
Ritsuka: well, is it possible to summon angels as servants?
Adam: that's rather random.
Ritsuka: I've been wondering that ever since I met King Hassan, and you're the only servant I know that actually met angels.
Adam: well, to answer your question, it's possible, but that depends.
Ritsuka: depends on what?
Adam: whether they want to or not. Angels, and I mean the ones that work for God, are higher mystics than even fae spirits. They can literally walk in and out of the Throne of Heroes whenever they want. But, even so, summoning one would be pretty impossible without extremely special circumstances.
Ritsuka: why is that?
Adam: because they're way too strong. King Hassan's connection to Azrael alone solidified him eternally as the Grand Assassin, so imagine if the REAL Azrael can be summoned.