Quite the interesting episode with a metric butt ton of information! Not only do we learn Yuliy’s past, we see his relationship with his brother, learn more about the enigma that is the arc, see a new vampire head honcho, develop Riyoko’s feelings a bit more, and reveal the professor’s past as well! Let’s dissect. 
The core of the episode revolves around Yuliy’s childhood. We’re introduced to a young Yuliy and his older brother Mikhail, the two have obvious chemistry and it becomes clear that the latter cares heavily for the former. Young Yuliy is characterized as idealistic and honest, but having a vulnerability to the cold. As for Mikhail, he’s basically Itachi, and awesome older brother. Yuliy seems to have grown up somewhere near Siberia, the Steppes, something along those lines. His traditional clothing could probably be analyzed to identify his approximate geographic location, but I’ll settle for a guess.
His village is called Dogville, which is likely touching upon his inner powers and possible werewolfish heritage. The village is quite small and not really populated, but they all seem like a bunch of happy campers. They drink and feast in the elder’s hut, and our brooding Yuliy actually seems happy back then. Unfortunately, vampires do what vampires do and ruin Yuliy’s life. Not only do they kill his mother, they wipe out his entire village, and take his brother Mikhail as well. Witnessing these horrors, Yuliy almost breaks entirely, giving up his will to live. Thankfully, the Professor arrives at a great time, saving Yuiliy’s life and convincing him to live.
The backstory itself was surprisingly touching, something I was not expecting when I first started Sirius the Jaeger. Yuliy’s past is ridden with tragedy and it’s caught up with him with the return of his brother. Mikhail’s fate is an absolute mystery, but the Professor thinks that Mikhail has entered a blood pact with the vampires. I’m unsure about this because Mikhail doesn’t seem like he’d do that, unless it was to protect Yuliy. He is quite literally Itachi if that’s the case, and it really pained to me to see him sacrificing himself for Yuliy’s sake.
Meanwhile in the present day, Yuliy is brooding once again. He’s guilty about two things, one that fact that he killed Dr. Hanada in front of Saki, and two, his joy of seeing Mikhail alive. It’s understandable that he’d be guilty about both, I mean Dr. Hanada was a good man and Saki and even better girl. I’m sure he’s extremely conflicted with himself about Mikhail as well, because he’s vowed to slay these vampires, but it’s very likely his brother is tied to them. Sirius the Jaeger is adding a layer of surprising depth to its action filled plot, and I really dig it.
The flashback also adds a bit of information around the arc itself, but not enough to actually clear the shroud of mystery around it. All we know is that Yuliy wants it, and that the vampires believe they need it to rule the world. We’re also given a bit of progression on the Riyoko Yuliy ship, which I’m still not fully on board with, but I’m not against it either. I just hope she doesn’t get built up as a potential love interest, only to be brutally killed or turned into a vampire. Oh god that’d hurt.
Overall, a great episode! Sirius the Jaeger is proving to be more than just an action filled, brain dead show, and I’m very happy about that.
I’d say I’m pretty impressed with Ryoko’s Resolve to be with Yuliy no matter what – she didn’t even flinch at seeing his fangs and glowing eyes. Especially since it’s such a ani/mangacliche that any girl would at least recoil a little.
PS. It seems in this universe, the vampires made their own Frankenstein’s monster as their secret weapon against the Hunters. I bet you they killed the original Dr Frankenstein for it. Or made him one of them. 😛