Challenging hike in late March/early April in Kansai, Kanto, or Chubu?

We’re going to Japan late March to early April next year and looking for recs for a challenging hike in Kansai, Kanto, or Chubu region.

It seems the Japanese alps won’t be open for hiking yet unfortunately. The person looking to hike does extremely challenging hikes in the US (mostly Colorado) so looking for tough hikes, ideally one that is scenic.

Thanks so much in advance!

by wonderfultravels