Non-commercial long 7 day retreats in Japan?
I'm looking for long and serious meditation retreats in Japan, at least 7 days (to 15/30 days). I know about Shukubo's but they appear more like a holiday with 2-3 hours of meditation, and most I found seemed commercial (charging much more than what a non-profit would).
I know about Goenka Vipassana obviously, but would be surprised if there are absolutely no other options with daily 7-8 hours of meditation for a week or more given that Buddhism is widespread in Japan.
EDIT: After @jpatokal's answer: While english instructions is definitely a plus, I'm happy to know about centers with Japanese only instructions too.
Pictures about "Non-commercial long 7 day retreats in Japan?"
The 10 Cheapest Countries To Live or Retire | You Might Not Need to Work
Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.
Images: Ron Lach, Quang Nguyen Vinh, Quang Nguyen Vinh, Erik Mclean