東都ラジオに努める小杉麻里（ReeSya）は会社からの指示で放送作家の山吹氷（杉崎智介）を訪ねる。山吹はトュレット症という精神疾患を持っており、加えて他人とのコミュニケーションが上手くできないという難点があった。戸惑いながらも麻里は氷と打ち解けていくのだが、ある日氷から「千年湯屋」の話を聞かされる。それはこの世とあの世の境にある不思議な湯屋であった。ところがその直後、氷は失踪する。縄文笛という不思議な笛を麻里に預けて。笛を頼りに麻里の冒険の旅が始まる。そして麻里が辿り着いた先は550年前の戦国時代であり、そこには変わり果てた氷の姿があった。氷を助けるためには麻里は過去世の記憶を呼び戻さなければならない。

Mari Kosugi (ReeSya) works at Toto Radio. Acting on a company request, she visits the reclusive radio scriptwriter Koori Yamabuki (Tomosuke Sugisaki), a man living with Tourette syndrome and struggling to communicate with others. Though hesitant at first, Mari gradually begins to connect with him.
One day, Koori tells her about the “Thousand-Year Bathhouse,” a mysterious place said to exist on the boundary between this world and the next. Soon after, he vanishes without a trace, entrusting Mari with a strange flute known as the Jomon Flute.
Guided by the flute’s call, Mari sets out on an extraordinary journey that leads her 550 years into the past, to Japan’s Sengoku era. There, she encounters a profoundly changed Koori. To save him, Mari must awaken the memories of her past life and confront a fate that transcends time and worlds.

歴史の記録は常に勝者の手にあります。敗者は悪として歴史の表舞台から葬られるのは想像に難くありません。しかし後世において歴史研究家や歴史マニア、あるいは作家によって、歴史の勇者がその雄姿を現代に示すことがあります。それは時代の要請でもあるのです。「こんな世の中に誰がした…」と恨めしく思うことが誰にでもあるのではないでしょうか。国を思い人を救い自らは大悪党として消えて行った人物は少なくないでしょう。日本が戦国時代と言われた15世紀から17世紀。その始まりに城つくりの天才、戦神（いくさがみ）と呼ばれた武将がいました。彼の名は長尾景春。その類まれな築城能力は現代の城址からうかがえます。しかしその人物像は正しく伝わっていない。また没年とされる後に各地の戦に参戦し大暴れした記録が多々あります。そして秩父熊倉山での見事な最期は伝説になっています。私は長尾景春の生き様に惹かれ、高校時代に熊倉山を歩きました。郷土資料館や土地の人たちに取材をし、私なりの結論にいたりました。それが本作『千年湯屋』です。この物語はファンタジーですが実際に土地に残る伝説をもとに書き上げています。にほんで唯一、あらゆる時代にいかなる落人をも匿った山の伝説を皆さんにお届けします。

History is always written by the victors.
It is easy to imagine how the defeated are cast as villains and erased from the main stage of history. And yet, in later generations, historians, history enthusiasts, or writers sometimes bring these so-called heroes of history back to life, revealing their true figures to the modern world. This, too, is a demand of the times.Tomosuke Sugisaki
Haven’t we all, at some point, found ourselves thinking, “Who made the world the way it is?”
There are many who loved their country, sought to save others, and yet vanished from history branded as great villains.
From the 15th to the 17th century, the period known in Japan as the Sengoku era, there lived a warrior at its dawn who was called a genius of castle construction and revered as a god of war. His name was Nagao Kageharu. His extraordinary talent for fortification can still be seen today in the remains of castles across the land. Yet his true character has never been accurately conveyed.
There are numerous records of him taking part in battles and wreaking havoc long after the year said to mark his death. And his magnificent final moments on Mount Kumakura in Chichibu have become legend.
I was drawn to the way Nagao Kageharu lived his life, and while still in high school, I walked the paths of Mount Kumakura myself. I interviewed local historians, visited regional archives, and spoke with people of the land, eventually arriving at my own conclusion. That conclusion became this film, RAIJIN.
While this story is a work of fantasy, it is rooted in legends that truly remain in the region.
We present to you the legend of a mountain—said to be unique in Japan—that sheltered all fallen warriors, from every era, without exception.