Japan's correctional system is considered safer than many others but it certainly has it problems.

Generally they are more like strict military prisons with highly strict and specific rules and regimentation. Punishment for violating rules may include loss of privileges and often having to maintain stress positions (aka torture) for hours across multiple days.

Reform is underway but as like as everywhere else it is making slow progress.

https://www.prison-insider.com/countryprofile/prisonsinjapan...