
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).
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.