A giant serpent and a giant centipede fought here — and the field became "the battlefield."

According to legend, the deity of Mount Nantai (Nikko) and the deity of Mount Akagi (Gunma) fought fiercely over the rights to Lake Chuzenji. Each transformed to do battle — Mount Nantai's deity as a giant serpent, Mount Akagi's as a giant centipede — and the fight dragged on with no resolution. The vast plain where this war was fought is said to be today's Senjogahara ("battlefield marsh") in Nikko, and that battle is the source of the name.

The turning point came from Sarumaro, a master archer allied with Mount Nantai's deity (or, in some versions, one of his descendants), who shot out the giant centipede's eye — its one weakness — finally routing the deity of Mount Akagi. Interestingly, a version of this same legend survives on the Gunma side too: the "Great Serpent Festival" at Oigami Onsen commemorates it, showing how one myth was carried and reshaped differently across two prefectures.

Lake Chuzenji itself is thought to have formed roughly 20,000 years ago, when lava from an eruption of Mount Nantai dammed the Daiya River. One reading of the myth is that it encodes a real memory of the mountain erupting and reshaping the landscape, later recast by later generations into the shape of warring gods.

The winding road up to Lake Chuzenji and deep Nikko, Iroha-zaka, is split into a one-way ascending road and a one-way descending road. Together they have exactly 48 hairpin turns — a number that matches the 48 characters of the classical Iroha poem (47 kana plus the character for "kyo"), which is how the road got its name. Each curve actually carries a sign with the next character in sequence, so drivers pass through the poem letter by letter as they climb.

The Iroha poem itself carries a meditation on impermanence: "Colors are fragrant, but they fade away — in this world of ours, nothing lasts." No matter how brilliantly a flower blooms, it will scatter; nothing in this world stays unchanged. It might just be a playful match between a number of curves and a number of characters, but the structure — inscribing one character of transience with every switchback — pairs surprisingly well with the sense of leaving the ordinary world behind as you climb toward Nikko's inner sanctuary.