Recapping in Chapter 1, you learned Ryoth was the god of eternal oblivion, aka the Void between dimensions. However, this isn't 100 percent true; he was still ruling over it after God banished him from his otherworldly domain, called eternal oblivion. Then he was sent to the Background, which was in the same place where he created Leon. God kicked him out of the dimension and into the background like a trash pit. In this case, the universe's Gods may banish beings from it, but also let them back in.
Eternal oblivion was a grueling afterlife for people who died after collecting all seven deadly sins, called: envy, pride, gluttony, greed, lust, sloth, and vengeance. People were left as souls without the ability to move and lost all senses for seven hundred and seventy-seven years. After this, they are given the chance for redemption. That person will be reincarnated with a hard life of their most dominant sin. If they had envy, then they were put into a life where they had many bad traits and expected to be grateful. For pride, a person was sent into the world experiencing lots of humility until they die. For gluttony, a person will be reincarnated into the world into a poor family that has little access to food. For greed, a person will be sent back to the world into a life a labor and no gain at all for their whole lifetime. For instance, a person will be sent back into the world infertile, with bad looks, and the inability to feel pleasure. For sloth, a person will be sent back into the world, born with birth defects, commonly born without limbs and other parts needed to move. If this person has changed after this torment of reincarnation, they may go to Heaven. If they still hadn't changed, they would have to keep repeating the processes over and over again until they changed into a better, selfless person.
In a universe with afterlives or other stages, it doesn't count as a multiverse. Instead, if a universe has Heaven or hell, then it isn't in the same place in the universe, but instead treated as attachments. When a universe dies, that doesn't mean Heaven dies, but instead lives on, leaving one massive paradise in place.
In eternal oblivion, there are giant winged serpents guarding the place to make sure no one else somehow gets in or escapes uninvited. If a being is caught inside, one that isn't in for redemption will be hunted and eaten alive. After the being is digested, they will be reincarnated as well without any memories of their background and how they died. Ryoth's purpose in the place was to send people out into the reincarnation process. After Ryoth was no longer in control of eternal oblivion, hell took its place under Satan's rules. In hell, things were only slightly different; people waited 100 years to start a reincarnation cycle to change them into better people. If they failed, they were tiruted to be taught a lesson and sent back again, and again, and again until they passed and were sent off the Heaven.