I could talk for hours about this topic. I lived in Japan for 10 years. It’s an entirely different dynamic over there when it comes to hiring a gentleman companion.
There are a few Japanese equivalents of RM, but if I were you, I wouldn’t even bother. Unless you speak and read Japanese, of course, but even then these are mostly college students and wayward former youths looking for money to buy PlayStations. A more discerning type of client will not find them appealing.
Instead, agencies are the way to go. And even then, “agency” is not the right word. It’s more of a “shop” from which you order delivery. There are many to choose from. (DM me and I can give a quick crash course in the niche Japanese vocabulary that will make choosing easier.) My all-time favorite, however, is a shop called Monster (link below). It’s literally a shop that specializes in male escorts (straight, gay, bi) with giant endowments. And lest preconceived notions of Asian male size convince you that I must be joking, there are PICTURES on the website. Monsters, indeed.
Monster 巨根専門売り専