I recently got to know this at the pizzeria Da Nino in Berne. I liked it, but when I looked it up on Wikipedia, I didn't find it there. I'm surprised it's associated with Japan, because it makes a very Italian impression! The flavour profile reminds me of the classic Italian aperitivo Cardinale, which is a 50-50 mix of Camparisoda and Aranciata amara.
Had a version of this at the Jigger and Pony in Singapore. Absolutely wondrous. I think they make it with Perrier grapefruit and some Nikka Coffey Gin too. Am trying to recreate it as can't find any shred of a recipe online.