In general, Turmeric contains curcumin, a natural Polyphenol. Curcumin is currently a hot topic in the research community because it has multiple health benefits, such as having inflammatory properties, helping the kidneys function, and improving metabolism. It is highly likely that Curcumin is the reason why Turmeric has been used as a type of medicine.
Japanese turmeric is a bit of a misnomer. On the one hand, there are several types of turmeric found in Japan, including wild turmeric (Kyou-ou), Okinawa Ougon Turmeric (Ukon), Spring Turmeric, and Black Turmeric (Gashutsu). These species are not exclusive to Japan, they can be found in other countries like China and India. These turmeric have anti-inflammatory properties which may help in managing Arthritis. You can get curcumin as a supplement.
On the other hand, there is a species of turmeric currently called Japanese White Turmeric in layman terms. What is unique about this species of Turmeric is that it is low in curcumin but high in labdane type diterpenes, high enough to be used as a supplement. There is some research showing that labdane type diterpenes are good for joint pain and there are some companies selling this turmeric extract as a supplement specifically for this purpose.
