Is a sleeping bag required in Northern Japan Alps mountain huts?

by Thomas
(Dresden, Germany)

Hi folks,

I am going to do the 6 day hike from Murodo to Kamikochi in the Northern Japanese Alps in about two weeks time. During the trip I am going to stay in mountain huts Unfortunately I can't find any information if I do need a sleeping bag. As I will stay in youth hostels in some of the bigger cities in Japan I'll take a light "mountain hut sleeping bag" which is rather a simple bed sheet. Now I'd like to know if this is good enough or if a proper sleeping bag is required.

Thanks folks!
Thomas