
This manhwa is turning into the very embodiment of Hyakki Yagyo(Night Parade of 100 Hundred Demons), there's so many ghosts involved, be it good or evil, all linked to the event/sentiment of the distant past. I think I might need to start making a characters chart or something to avoid more confusion lolol.

Since the translation didn't caught up to the latest raws yet, I can only screen translate and read some comment in other language in other website, which is not 100% accurate, so take this with a grain of salt.
Characters chart:
Jeong Yitae(Manager of Giyoon and Na Jumin in present days): successful reincarnation of Muni's Young Master as the result of the second ritual. His ghost past self(Young Master) clings to him. Both had different personalities and he doesn't share the same trait with the original Young Master.
Giyoon(glasses MC): successful half reincarnation of Muni, servant of Young Master. The calm side of Muni that Young Master want when he performed the ritual with the shaman in the past.
Na Jumin(Giyoon's coworker): another half of Muni's reincarnation. Actually he is the original Muni successful reincarnation, who likes human Jeong Yitae in present days. This is the side of Muni who loves Young Master one-sidedly in the past. Share many traits with original Muni.
Evil Ghost Snake Muni: evil ghost borne out Muni's failed reincarnation ritual attempt in the past, performed by the Shaman, by the request of the original Young Master. Long ago, Young Master made a request to a shaman to reincarnate Muni in a new reincarnation(body), using forbidden ritual that combined a snake and Muni's blood/corpse. This ritual failed and created an evil ghost instead who hate and despise Young Master. This snake ghost was the one who made a deal with Giyoon(MC) for him not to remember the past about Young Master and to ignore supernatural occurrences around him.
Young Master Ghost(Muni's Master): past self of Jeong Yitae. He made another ritual/sacrifice to maintain/bind his existence in present days by sacrificing lots of people/underling. That's why there's so much ghosts(victim of ritual sacrifice) who clings to Giyoon, some is loyal to Young Master, and some despise Young Master who prevented them from moving on to the afterlife.
Yuran(Giyoon's coworker): Descendant of the shaman who performed the ritual for Young Master. Inherited her spiritual sense from her ancestors.
To make this matter easier to understand, for those that watch/read Harry Potter series, we learned that Voldemort split his soul into 7 parts, thus creating 7 Horcruxes. Similar case happened in this manhwa, with Young Master performing a ritual to split Muni's soul into 3 parts, with each soul becoming different individual entirely(Giyoon, Na Jumin, Snake Ghost).

Even though I hate the military's judgement here, considering in the novel there's a case where an infected students escape much earlier and mutate inside a rescue truck and proceed to bite another soldier, so their superior's order must have change to "shoot on sight". There's too much risk involving rescuing a survivor after that incident and the whole campus area was sealed off for good after that incident.
Though if they really wanted to impose a blockade, they might as well bomb the entire campus area so there's no survivors or infected individuals, effectively burying the whole incident. I'm not agreeing with the military, but this is one of those situation where "small sacrifices for a greater good" type of situation, although it was very much inhumane. If you guys were wondering, there's a group of survivors which escaped the campus much earlier in the story, before the enforcement of the blockade, but some of them was of course already infected, causing a wide spread incidents across the nation.

From the what I understand thus far, this story involves some of the most powerful mythological creatures in Korean culture that is Dokkaebi((Goblin)Easily the most poweful creature amongst other mythological beings) and Kumiho(Nine-Tailed Fox). It also depicted the surface level of Korean Shamanistic belief such as the use of Jangseong(Guardian Spirit Totem Pole) and maybe some deity like Samsin Halmeoni(Grandmother Samsin(Similar to Hariti or Hecate)).
In other similar Korean folklore story, be it BL or not, we've already seen a creatures like Yong(Korean Dragon), Pulgasari/Bulgasari(Metal-Eating Beast), Imugi(Lesser Dragon Serpent-Like Being) and even some important figures like Joseung Saja(Grim Reaper) and Yeomra(King of Underworld).
Confining Immortal Rakshasa in a secluded space? Ever heard of Akabane Kuroudo who had reality manipulation sword that can cut through time and space? Yeah I'd imagine Immortal Rakshasa had the similar power like Divine Providence which allows him to warp reality in some ways that he imagine it to. Props to Maru for thinking this brilliant strategy, but if it is that simple, original Space Rakshasa can just confine every single one of the 8 Guardians without him needing to create an army in the first place.
One thing about this story is they are only given the power of what's within their title. I.e., gluttony rakshasa will only have the power to eat and absorb the powers of those he ate. The space rakshasa, another one of the guardians, only had the power to manipulate space, no matter how OP he was, he didn't have anything that wasn't connected to space manipulation. He's the immortal rakshasa so his power is mostly limited to being immortal, hence regenerating even from a drop of blood. The immortal rakshasa suddenly being able to warp reality despite just having the ability to be immortal, seems out of the specs of the world's rules and reality
Also, I'm pretty sure the reason why Space Rakshasa didn't confine them in the space realm because the only way to go in and out of the space realm is if the Space Rakshasa opens a portal and Jeong Ildu used to open a gate every time he would need to summon other rakshasa that he's imprisoned or when he's imprisoning other rakshasas. Just like in Han Maru's time there where he only got out because somewhere in the realm, Jeong Ildu opened up a portal to summon a rakshasa he's been keeping there. Jeong Ildu would've had to open up a portal each time he transports one of the 8 heavenly guardians or even one of the rakshasas he's imprisoned so it wouldn't have worked out as one of the 8 would've gotten out as well. That's why he only stored normal rakshasas there as they aren't that big of a threat and wouldn't likely be able to find the random portals he summons. Unlike Jeong Ildu, Han Maru wouldn't use the space realm aside from transporting this immortal rakshasa so it could be a good plan.