I ended up looking at some of the suits on the real Japanese Aqux site. The exchange rate with the yen is currently 133 Yen to the dollar which means a suit costing 7600 yen would be about $57 US$
A lot of the briefs are cut very low so that they intentionally show some upper butt crack. see this one to illustrate
https://aqux.ocnk.net/data/aqux/prod...713_9ba0f0.jpg
sort of the unwritten rule in the US is that the swim brief should be cut high enough to nit show any butt cleavage but In Japan this appears to be part of the style and look for the guy.
Keep in mind that a SM in Japanese sizes is only 24-26 inches in US measurement, MED Japanese is 26-28: and Japanese LG is actually US SM at 28-30 inches. And the waist size is lunked to the rise of the suit.
My no longer available Chinese sourced "Aqux" suits were of very high quality both fit and material and remain in excellent condition. These were not an inferior product at all but I can understand why they are no longer available if they were in fact an unauthorized copy.
Anyhow the real Aqux site is fun to visit, and here is a link for some of the suits there. Check out the rear fit on the suits.
https://aqux.ocnk.net/product-list/9