While its pretty nice, all I can think about is how damn annoying that hair would be lol - you'd both be getting all tangled up in it like that! You'd have half of it yanked out too, and all knotted.
Mostly you just fit the two people into a normal sleeping bag. It's entirely doable. Hell, in cold enough environments (which Japan does not have, outside of the tops of certain mountains) it's actually NECESSARY.