Mt. Oasahidake

Mt. Oasahidake (大朝日岳, 1,871 m), straddling Nishikawa, Oe and Oguni Towns in Yamagata Prefecture, is the principal peak of the Asahi range within Bandai-Asahi National Park — known in Kyūya Fukada’s “100 Famous Mountains of Japan” as “Asahi-dake” (the namesake of the Asahi mountain range).

Called the “Tōhoku Alps”, the Asahi range has the most extensive beech primeval forest in Tōhoku and famed Hime-sayuri lily fields (Lilium rubellum, early–mid July) along the ridge, with 360° panoramic summit views to Mt. Gassan, Mt. Chōkai, the Iide range and the Zaō range. The standard Kodera-kosen course and Asahi-kosen course are advanced ★★★★★ / 18 km / 1,750 m gain / 1-night 2-day plan with Oasahi Hut overnight recommended.

*Timetable last checked: May 22, 2026

How to access the trailheads

1. [Round trip] Aterazawa Station ⇔ Kodera-kosen / Asahi-kosen (summer climbing bus / taxi)
2. Kodera-kosen course, Oasahi Hut, suggested plans

Standard times (Kodera-kosen course, 1 night 2 days, advanced, ~12 hours)

Day 1 (~6 hours): Kodera-kosen (670 m) → (2:00) → Kodera-yama (1,500 m) → (1:30) → Ko-asahi-dake (1,648 m) → (1:00) → Gingyokusui → (1:30) → Oasahi Hut (1,820 m, below summit), overnight

Day 2 (~6 hours): Oasahi Hut → (0:30) → Mt. Oasahidake summit (1,871 m) → (5:30) → Kodera-kosen (return)

1. [Round trip] Aterazawa Station ⇔ Kodera-kosen / Asahi-kosen (summer climbing bus / taxi)

From Aterazawa Station to the trailheads: Asahi-kosen (Nishikawa Town side) is reached by Asahi Climbing Bus in about 1 h 15 min, 1–2 runs/day in summer (2026 only open from Niigata side — confirm); Kodera-kosen (Oe Town side) is by taxi only, about 50 min for ~¥10,000. Oe Taxi (☎0237-62-2155) offers climber plans with drivers familiar with the Asahi range. Self-drive: ~30 min from Gassan IC or Nishikawa IC on the Yamagata Expressway.

Operating period : Asahi Climbing Bus summer (typically Jul–Sep, 2026 confirm), Kodera-kosen by taxi year round
Travel time : Aterazawa → Asahi-kosen about 1 h 15 min (bus) / Aterazawa → Kodera-kosen about 50 min (taxi)
Fare : Asahi Climbing Bus ~¥1,500, taxi ~¥10,000 (Kodera-kosen)
Frequency : Asahi Climbing Bus 1–2 runs/day (summer only)

Aterazawa Station → Asahi-kosen (Asahi Climbing Bus, summer-only, hiker excerpt — 2026 confirm)

Asahi-kosen → Aterazawa Station (Asahi Climbing Bus, return, summer-only)

Note : The 2026 road repair on the Asahi-kosen approach means operation and access may be restricted — always confirm with Asahi-kosen official or Asahi-kosen Naturalist Lodge ☎0237-67-2860. The Kodera-kosen route is stable. After descending, bathe at Oisawa Onsen “Yuttari-kan” (¥300).

Reference : Asahi-kosen access ｜ Oe Taxi Asahi range climbing
Inquiries : Asahi-kosen Naturalist Lodge ☎0237-67-2860 / Kodera-kosen Choyo-kan ☎0237-67-2226 / Oe Taxi ☎0237-62-2155

2. Kodera-kosen course, Oasahi Hut, suggested plans

About Mt. Oasahidake
The principal peak of the Asahi range (1,871 m) in Yamagata Prefecture, within Bandai-Asahi National Park. Selected by Fukada as “Asahi-dake” in his 100 Famous Mountains (the namesake peak of the entire Asahi range). Called the “Tōhoku Alps”, it features the longest ridges in Tōhoku, the most extensive beech primeval forest in Tōhoku, the famed Hime-sayuri lily ridge fields (early–mid July, endangered species), and a 360° summit panorama over Mt. Gassan, Mt. Chōkai, the Iide range and the Zaō range.

Trail summary (3 main courses)

• Kodera-kosen course (Oe Town side, standard, advanced, ~12 h, 1 night 2 days): Kodera-kosen → Kodera-yama → Ko-asahi-dake → Oasahi Hut → summit out-and-back, through beech primeval forest
• Asahi-kosen course (Nishikawa Town side, advanced, ~12 h, 1 night 2 days, 2026: only open from Niigata side): Asahi-kosen → Torihara-yama → Ko-asahi-dake → Oasahi-dake
• Ito-dake traverse (advanced, 2 nights 3 days): full Asahi range traverse

Huts and hot springs (2026 information)
– Oasahi Hut (below summit, 1,820 m, no phone): for-fee (cooperation fee ~¥2,500), manager resident Jul–Sep, bring bedding and food, toilet, capacity ~80. Outside the staffed period, usable but unmanaged
– Asahi-kosen Naturalist Lodge (trailhead, ☎0237-67-2860): lodging ¥9,500+, self-cooking ¥6,000+, best climbing base (2026 access by road repair — confirm)
– Kodera-kosen Choyo-kan (trailhead, ☎0237-67-2226): lodging ¥10,000+, climbing base
– Oisawa Onsen “Yuttari-kan” (¥300, after descent)

Climbing season / flowers: mid-June to mid-October. Early–mid July: Hime-sayuri lily fields (endangered, ridge), Hakusan-ichige, Nikkō-kisuge. Late September – October: autumn colours and beech yellow. Residual snow on the ridge and around Gingyokusui until early June.

Cautions
– 2026 Asahi-kosen access road under repair: use the Kodera-kosen route or confirm with Asahi-kosen
– 1 night 2 days (effectively required): 12-hour course, not a day hike, Oasahi Hut overnight
– Limited water: Gingyokusui and Kingyokusui (near Oasahi Hut) only — carry at least 2 L
– Bear sightings common: carry bells and pepper spray, watch for scat
– No picking Hime-sayuri: MOE Red List, Yamagata Prefecture protected

Emergency contacts and inquiries

• Nishikawa Town Hall (Asahi-kosen side): ☎0237-74-2111 / Oe Town Hall (Kodera-kosen side): ☎0237-62-2111
• Oguni Town Hall (Iwa-i-bachi-yama, south side): ☎0238-62-2111
• Sagae Police Station (climbing plan, mountain rescue): ☎0237-86-0110
• Asahi-kosen Naturalist Lodge (lodging): ☎0237-67-2860 / Kodera-kosen Choyo-kan: ☎0237-67-2226
• Oe Taxi (Kodera-kosen transfer): ☎0237-62-2155

Suggested plan (Kodera-kosen course 1 night 2 days, recommended)

• Day 1: Tokyo 6:00 → Yamagata 9:00 → Aterazawa 10:00 → Oe Taxi → Kodera-kosen 11:00 → Kodera-yama 13:00 → Ko-asahi-dake 14:30 → Oasahi Hut 17:00 overnight
• Day 2: early summit 6:00 (sunrise, 360° view) → descend → Kodera-kosen 12:00 → taxi → Aterazawa 13:00 → Oisawa Onsen bath → return
• For the Hime-sayuri lily bloom (early–mid July), book Oasahi Hut a month in advance

Reference : Asahi-kosen official ｜ Yamagata Pref. Mt. Oasahidake guide

Photo by Wikimedia Commons