Here it is. The best climb in Hokkaido. I'm not kidding about that. However: it looks like sometime in 2016, a huge flood demolished much of the road leading to the trailhead at Juuroku-no-sawa, so much of what I've written about the approach is, for the moment, untenable.
For some coverage of the road damage, see images here.
It looks like you can park your car outside the gate and walk in. This is obviously a more dangerous route to take to the mountain, but if you're experienced and determined, it's an available option. It appears to take 2.5 hours to get from the gate to the trailhead itself. If you look in the mountain ledger, you'll see other people have walked in to hike the mountain--and the trail itself appears to be intact.
I wouldn't recommend it.
Mt. Nipesotsu-yama (ニペソツ山, Nipesotsu-yama) stands northwest of Lake Nukabira (糠平湖, Nukabira-ko), huge and pointed like the prow of the Southern Daisetsuzan. From the approach across Tengu Plateau (天狗平, Tengu-daira) the mountain rears up before you like almost no other. The snow on the slopes in early summer only highlights its sheer face. The mountain has a gentler side as well: the fields along the broad ridgeline towards the summer are rich in wildflowers, and eagles make their nests in the trees surrounding the marshes. You wouldn't be the first to remark that the whole journey up resembles an imposing approach to a medieval castle.
The mountain’s name comes from the Ainu nipesh otsu, meaning “[place with] many Japanese lime trees.”
There are two trailheads: one from the Otofuke River (音更川, Otofuke-gawa) Juuroku-no-sawa (十六ノ沢, lit. 'No. 16 Beck'), and one from Horoka Onsen (幌加温泉) further down the eastern slopes of the mountain. In this guide, we'll head up the Juuroku-no-sawa Trail, both because it's slightly shorter and because it offers a broader variety of scenery.
To get to the trailhead, take National Route 273 (国道273号線, kokudou 273 gosen) to Tokachi-mitsumata (十勝三股) district, and take the turnoff into the wooded road following the Otofuke River, keeping to your left as you go. There's a convenient wooden sign with the names of all of the mountains that this forest trail serves (alas, like most things in Hokkaido, they're only in Japanese). As of May 2018, the road to the trailhead doesn't appear on Google Maps, but you can spot it on satellite view.
After gaining a little elevation, you’ll find the trailhead near where the Juuroku-no-sawa meets up with the Sugi-sawa (杉沢).
From the trailhead, you’ll cross the Juuroku-no-sawa and head up into an evergreen forest typical of the Eastern Daisetsuzan. Dark, Christmas-smelling, and a steep, steep climb. Soon you’ll find yourself climbing a ridge of the Nipesotsu massif as the forest transitions from evergreen to Erman’s birch. From here the trees will open up and you’ll find great views of Mt. Upepesanke-yama (ウペペサンケ山, Upepesanke-yama) to the south. In the fall, the red leaves of the tail-leaf maple and the Tschonoski snakebark maple should make this a very pleasant climb.
At the top of this ridge, you'll round some bluffs south of Mt. Kotengu-dake (小天狗岳, Kotengu-dake), and head on toward the subordinate peak of Mae-tengu (前天狗). Along the way, you'll drop into a marshy saddle called Tengu Col (天狗のコル, Tengu-no-coru). There’s a small campsite here, with space for maybe three tents. Water can be had from nearby snowmelt until about mid-July.
You’ll climb back up onto a steeper ridgeline on your way to Mae-tengu. As you enter the forest of dwarf stone pine, listen for the cries of the minute pika coming from the crags around you. Near the top of the ridge the trail branches and winds variously and the Horoka Onsen Trail merges, before all reconnect around the Mae-tengu summit itself.
By this point you probably won't have come face to face with Nipesotsu itself. But after a dip down past Mae-tengu and then a climb back up Tengu Plateau, you will. It will stand before you like the prow of a huge ship coming your way. Tengu Plateau is a great place to stop for a rest before rushing the summit. Enjoy the views dropping off to the east; the slopes tumble down some 600 meters (that's two Eiffel Towers) to the headwaters of the Horoka River.
Once you're ready, follow the trail along the western flank of Mt. Tengu-dake (天狗岳, Tengu-dake), drop into a col, and start the hard last climb. Down the perilous eastern flanks of the mountain, you’re likely to see Kamtchatka globeflower, Alaskan arnica, and blue mountainheath growing in the wind. Soon the trail will round the cliffs and come north, and shortly thereafter you will find yourself at the summit of Nipesotsu-yama.
Though the summit itself is very narrow, the sky above will be immensely wide. As the summit affords more or less 360-degree views, you’ll probably be able to spot the mountains of the central and southern Daisetsuzan with ease. Mt. Asahi-dake should be visible well in the distance, lined up neatly with Mt. Tomuraushi-yama (トムラウシ山, Tomuraushi-yama) and the Tokachi Range (十勝運峰, Tokachi-renpou) as you proceed south. If the air quality is really good, you should be able to see Mt. Shari-dake (斜里岳, Shari-dake) far in the northeast, and the mountains around Lake Akan (阿寒湖, Akan-ko) in the east.
If visibility isn’t great, be very careful as where you sit and step as you head down. The ground is loose and the drops are fatal.
You’ll head down along the same trail you came up. Though you may be heading down in a hurry, we recommend stopping for a moment near Tengu-dake or Tengu-daira to listen to the pika. In the fall, the deep red of the alpine bearberry is beautiful.
The forest blooms with green in late June and early July. In late August you’ll be able to see such flowers as autumn dwarf gentian, Kamchatka rhododendron, bog-star, Thunberg’s fleabane, and Yanagisawa’s narrowleaf saw-wort. The leaves change color in mid-September. The first snows come a little later here than in the Daisetsuzan proper; if you’re thinking of hiking around the first snows, make sure to bring adequate cold- weather gear, since the walk along the ridgeline can be a long and cold one.