On a rainy day Ginko takes a rest from his travels and comes across a man named Kourou who seems to be obsessed with a rainbow. To pass the time Kourou reminisces in his past, with the events which led to him pursuing rainbows whenever they appear. Ginko explains to him that the rainbow which he is searching for is actually a Mushi known as "Koda" but there seems to be more to it.

Ginko arrives at a village where the men are in a heated discussion about the mountain. After learning of Ginko's identity they ask for his help to find another Mushi-shi called Mujika, who happens to be the master of the mountain. While on his trek through the mountain Ginko stumbles across a boy who's also looking for Mujika. Later they manage to find Mujika but this isn't the end of it.

It is spring, and Ginko is taking a boat through a river, when the boat's boy, Kaji, asks Ginko whether he could help his mother, who's forgetting things and can't sleep. At first glance it may appear to be progressive amnesia, however something isn't right.

"There are countless fissures in the physical world. Those who vanish like smoke are lost in such hollows. Without their memories, without their souls..."

Ginko receives a letter in a cocoon, but it isn't adressed to him. Rather, it's addressed to an old accquaintance, Aya Tozawa, so he decides to visit her. Ginko is concerned about Aya, as she is still searching for her sister, who has been trapped in an Uroana for 5 years.

Ginko arrives at a secluded place, to meet an old acquaintance, who seems to be in charge of a large volume of archival, confidential text. Ginko is allowed to read it, and discovers it is the work of Tan'yu, a writer. Tan'yu is the descendant of the Karibusa family, being born with a black mark on a part of their body.

A lady named Aki discovered a green stain on her wedding gown, one year later she gave birth to a boy who, now grown up, has the same marks on his body. It turns out that the boy was originally born not as a human but as some shapeless green blob, which then turned into a human. Her husband asks for Ginko's help yet he is unable to save her son because it's the work of a "Watahaki".

Taku is a peculiar young boy who has always wondered who the people were that always passed by the mountains during the rainy seasons. One day he meets a boy named Isaza, while catching fish. It seems that not only Taku can see the Komiyaku in the mountains however Isaza seems to know a lot more about the mountain than him.

"The world is filled with life unknown to man..."