What exactly is Sleep doing throughout this match? https://www.youtube.com/watch?v=OU92R9uWedA Can you describe in detail everything he's doing here?

You can tell that Sleep knows Kan-Ra's strengths and weaknesses pretty well by this video. There are things he does that other players who are less familiar with Kan-Ra tend not to do (for example, anti-airing Kan-Ra at 0:24 and the exact same situation comes up again at 5:20, 7:52).
But for the most part, he's just really patient. He's willing to block for long stretches, because he knows that Kan-Ra has to take a risk with command grab; since Aganos is so tall, he can't put scarabs above his head and strengthen the mixup, since Aganos will block the scarabs due to his height. The start of the 2nd match at around 2:20 is a good example of his patience. Sleep simply blocks a lot, building a lot of meter, and then picks his spot with either a shadow Ruin or shadow Pulverize and then builds up some more chunks. Kan-Ra actually isn't very much of a threat if he can't set up scarabs above your head, as long as you're able to block the jump fierce shenanigans and make 50%+ correct reads on his command grab (I think Sleep was trying to react to the 20 frame startup of the command grab, which is definitely possible). Remember, KI doesn't have a ton of chip damage, so simply blocking for a long time is actually a pretty good idea. You build a ton of meter for blocking and maybe lose 2-3% life at most, and Aganos is at his most threatening with shadow meter, so this strategy is the best idea in this fight.
For example, take a look at around 3:45-4:10, where Sleep chooses to block a ton of sand spikes + antlions. He's taking virtually no chip, but he quickly gains a bar, and now Kan-Ra has to be nervous. He has similar patience at around 8:10. He knows he has the advantage here with 2 meters and Kan-Ra eventually having to do something with long recovery to get any damage, so he just slowly walks forward, blocking regularly, knowing he doesn't have to throw his face into a bunch of damage.
I think long term people will find that this match is actually quite even, or maybe even favoring Aganos. From full screen, Aganos is actually quite a threat. Not counting his rock zoning, which can be self-sustaining, you can see a sneak peek at 10:58 when Sleep rolls through a spike attempt (but drops the combo). If Aganos does MP natural disaster and presses up, he can avoid both spike and antlion and start a combo, and if he's not willing to take the risk, he can block and get full bar for shadow Ruin later. Meanwhile, Kan's full screen threat is more smoke and mirrors than it seems.