I've found this matchup to be quite tedious for Azrael. From my little experience when facing any Relius player, he plays at a distance until he gets pressure, then closes in, mixes me up using both his Ignis normals and his own. I'm not too great a player really, but it seems like Relius has the upper hand when it comes to getting in. However, in the event Azrael lands a hit and begins his pressure, albeit short pressure, Azrael has the upper hand at close range. At this point Relius players may begin to rely on 236A, which loses to throws, meaning if read then it can be punished for good damage (5.4K at most with 50% tension and double weakpoints). I'm not too much of a great player right now, so I can imagine most people might be thinking a bit differently. This is all entirely my opinion. Though I did find some stuff that may be slightly useful.
-- Azrael 5C at max range can either beat or trade with Ignis wheel.
-- Relius meter reversal can lose to Growler. Gives Azrael stock and plenty time to punish with a big CH combo.
-- Azrael 5C can also beat Relius' 214C easily.
-- Azrael can Growler Relius' 22A/B/C, any of them.
-- When on the ground, Azrael 2C can beat Relius' jA if timed properly, jB, and jC. 6B can also beat jA easier than 2C can, it can also beat jC. 6B has a chance to clash with jB, so I found it much simpler to stick with 2C.
-- Azrael 2C can somehow not hit Ignis j2D, but at the same time Azrael does not get hit either. I'm not sure if this is really too reliable. In this situation, 6B seems to have better reward.
-- Azrael will most likely lose in any air-to-air situation. Use Gustafs and other stuff to get in, but don't be too reliant on it or Relius can and will punish it. Bait out Ignis normals and wait for him to decide he needs to recharge the meter, then find a safe way to approach him. Even without Ignis, he can hit you out of the air with 6B for a free combo.
--Relius players seem to love the air (though remember I have not faced many of them). 2C quickly fixes them.
I should also note I'm still a beginner myself, so some of this stuff may seem really silly. I apologize for that.
When it comes to this matchup, you need to stay in Relius' face since Azrael can't do much at a distance aside from BHS and gustaf, and the last thing we want is a baited BHS. Relius does not have very many defensive options, so he loses if Azrael touches him. Most Relius players will use their meter reversal or in rare cases 236A to get out of pressure, you can punish his super on block, and 236A is not throw invulnerable as I've said before. What Azrael can do at a distance is bait out Ignis normals and get Relius to start being cautious, therefore making him defensive, the last thing he wants against Azrael. Some Relius may resort to mashing, so be careful on that.