The second GoPro accessory I bought from Bic Camera at Aqua City Odaiba is the GoPro Hand + Wrist Strap.
It retails for JP¥5,819 (S$73), excluding tax.
After the 7% discount from the Klook Bic Camera Tourist Privilege Discount Coupon in Tokyo, I got it for JP¥5,411 (S$68). In Singapore, the official retail price for it is S$85.
This accessory comes with a rotating mount and two straps (hand strap and wrist strap).
The rotating mount allows you to adjust your GoPro’s capture angle on the fly by rotating or tilting your GoPro. Since it can be rotated, you can use the hand strap on either your left or right hand.
Both straps should fit the wrist and hand of most adults and they are waterproof (so you can use it in waters).