Kotaku (こたく Kotaku?), or Shinsenkyō (神仙郷? Literally meaning: Divine Paradise), is an island located within the seas of the southwest which supposedly holds the Elixir of Life. The island is under the rule of seven immortal beings called Lord Tensen and acts as a giant laboratory for experimentations dealing with immortal life. Kotaku is the main setting throughout the series.
Over 1,000 years ago, Xu Fu attempted to unlock the secrets of immortality for the emperor of China and concluded that the Elixir of Life is located on the three islands known as Eishū, Hōjō, and Hōrai. He then sailed off with a large fleet but was reported to have went missing in his pursuit. Despite the report, Xu Fu remained active and merged the three islands together through unknown means, creating an artificial island known as Kotaku and acted as its ruler. Xu Fu continued his research by experimenting with Tao, resulting in the creation of fabricated species, and as time began to catch up with the Hōshi, Xu Fu left the responsibility of creating an Elixir of Life to a group of humanoid monsters who call themselves Lord Tensen.
While taking up their master's legacy, Lord Tensen served as the new rulers of Kotaku. Together they trained in the ways of Taoism in Hōrai and guided the island's inhabitants known as the Hōko using fabricated beliefs in order to secretly observe their way of life and use them as resources to replenish any Tao they lost. They also acted as Taoist teachers to the Dōshi. After 200 years passed, the Hōko started to undergo Arborification and were guided by their beliefs to enter Hōrai in order for their souls to lay to rest. This caused the young members of Lord Tensen to go into a panic after losing their Tao resource and decide to use humans from the mainland as a replacements by luring them in with an Arborified Hōko.
After several centuries, Lord Tensen managed to lure in the first group of humans to the island and discovered how the human race's Tao after ambushing them. From then on throughout the ages, Lord Tensen began to extract the Tao of the humans that came to the island, and as a result, they managed to create the prototype elixir known as Tan that would supply them with endless amounts of Tao until they finally manage to create a perfected Elixir of Life. Rien also made use of the humans to create the Banko within his laboratory to produce a far greater quantity of Tan.
Kotaku derives from two religions: Taoism and Buddhism. The man-made statues on the island combines these two religions, although according to Senta they are executed poorly. The Sōshin also take attributes from these religions.
Kotaku is divided into three regions: Eishū, Hōjō, and Hōrai.
Eishū (えいしゅう Eishū?) is the outer region of the island, which holds the forest and the beach. The forest is covered in plant life, mainly due to the blooming corpses of samurai that last ventured the island. The Sōshin are stationed in Eishu to eliminate any trespassers.
- Further information: Hōjō
Hōjō (ほうじょう Hōjō?) is the second region of the island. Hōjo is a valley that circles around Hōrai and where the Sōshin nest. The Hōko once resided in Hōjō in a small village 1000 years ago until they underwent Arborification, leaving the village in ruins. Years later, Hōko and Mei became the only known people residing in the village.
- Further information: Hōrai
|Gui Fa||Ju Fa †||
Mu Dan †
|Tao Fa †||
Zhu Jin †
|Lettuce Dōshi *|
- In Senta's opinion, because Kotaku takes religions from the outside world, it cannot be viewed as Shinsenkyō.