This is one of the most popular mountain huts among locals. They are known for their dinner steak.
About:

Located at an elevation of 2,220 meters in the Japan Alps, Akadake Kosen Mountain Hut offers a cozy retreat for hikers and climbers. With a capacity for 300 people, guests can enjoy a night's stay with two meals for 13,000 yen per person. The hut also provides options for dinner-only or breakfast-only stays. For those looking to pitch a tent, there is space available for around 50 tents at 2,000 yen per person.

Reservation page: https://www.akadakekousen.jp/reservation-form-for-inbound-guests