The strange arboreal monster introduced alongside Mei in Hell's Paradise: Jigokuraku episode 7, Hōko, revealed a great deal of information to Gabimaru and the group, including some much-needed information on the nature of the Elixir of Life, and the structure of the island that Hōko and Mei call home. Given that he was born on the island and has lived for over a millennium, Hōko's intel is invaluable to the group and brings them much closer to locating the legendary elixir.
When asked about the location of the source of eternal life, Hōko draws them a simple map of the basic layout of the island. Here's Hōko's brief rundown on the very structure of Shinsenkyō, otherwise known as Kotaku.
Layers
Given that the narrative of Hell's Paradise: Jigokuraku has inspirations in literature and mythology, the concept of Kotaku is largely a reinterpretation of some mythological and religious concepts. Kotaku and its three layers, as well as the Tensen are inspired by the Eight Immortals in Chinese mythology, and the island is partly inspired by the utopian island that they lived on. Having lived on the island for over 1000 years, never having left, Hōko's understanding of its structure is sure to be reliable. He explains to Gabimaru and the group that the island is divided into three regions, drawing a basic concentric circle to give his words visual representation. The forest that makes up the outer part of this island is known as Eishū, and this is where people are most likely going to encounter flowery landscapes and the various abominations that have been seen on Kotaku thus far.
These monsters are known as the Sōshin and are the lowest class of monster on the island, serving as guardians for the far more valuable, and far more elusive inner regions of the island. The village where Hōko and Mei live is located in the second region known as Hōjo, which is a valley that lies beyond Eishū. The Sōshin come to nest in th island, while the most important region of the island, Hōrai, is the location of the Elixir of Life. As expected, Hōrai is where an encounter with the superior beings known as the Tensen that Hōko tells the group about is just about guaranteed. They guard the very secrets of eternal life, each having walked a different path towards immortality.
Eishū
Characterized by extremely beautiful or extremely grotesque scenery depending on who you ask, the outermost region of Kotaku is scattered with dazzling flowers of varying kinds. The colourful landscape hides the dark secret of the island and the secret to eternal life that is located there, with the flowers each blooming from the bodies of unfortunate visitors to the island. The dangerous fauna and Sōshin that guard the island from all foreign entities make surviving Eishū essentially impossible for the average person, and it is for knowledge of such abominations that the shogunate sent criminals who have exceptional abilities of some kind, to increase the extremely slim chances of success.
Hōjo
The middle point separating the outermost Eishū from the island's innermost region is Hōjo, which was the home of a thriving population over a thousand years ago prior to an incident that saw the extinction of various kinds of life on Kotaku, including the people who once lived there. Now, Hōjo is inhabited by Hōko and Mei, who simply want to live in peace. The desolation of Hōjo is extremely apparent, with the ruins of Hōko and Mei's village serving as one of the few points of interest as a thick fog blankets the area.
Hōrai
The middle of the island is known as Hōrai, where the legendary secret of immortality can be found, as well as the gods said to inhabit the island – the Tensen. This part served as the base of operations of Jofuku, a man who was sent to the island from China by the then emperor of the Qin dynasty several centuries prior to the events of the story of Hell's Paradise: Jigokuraku. Jofuku's objective was to find the Elixir of Life; however, instead, he found Kotaku and devoted himself to discovering the secret to immortality. Nothing about the landscape or layout of Hōrai is known to any of the main characters just yet; however, given that Hōjo showed increasing signs of civilization compared to the island's outermost part, it may make sense to expect more artificial structures like buildings, rather than the various statues that are littered across Kotaku.