Most banana skin are edible. We just don't get use to eat it ,because somewhat it does not have good taste . Beside, most bought bananas have heavy chemicals on its skin,so it is not good for eating. Back in Viet Nam, my Grandfather used to sun dried bananas with its skins on. I ate sun dried banana with skin on as a kid and I like it.
As for The Mongee Banana in Japan. They freezed the young banana plant and then replanted it. This technique cause the plant to produce a thin banana skin. The look of banana skin and the description somewhat remind me of an over ripe banana with brown spots. This article have more information about Mongee Banana
https://japan.mb4uli.com/tag/edible-fruit-skin/