Most Japanese will use nothing synthetic, and if they do use oil it will be 100% natural (99% of the time), but it wont just be 100% oil, for example, Minorien's Fu-in range (lets take the Aloeswood stick for an example) they use a couple raw aloeswoods with some natural in house aloeswood oil of a high quality at a very low percentage, to create more of an oudy scent with their signature "wet" feel. Then you have low range Nippon Kodo sticks that use just pure synthetic oils, but I think that is the only Japanese house that does so, the higher you get in ranges with Nippon Kodo the oils become natural and the use of raw materials are used more and more until you get to the very highest range, were oils are still used but are natural and more raw material is used. Tennendo, like the amazing Tensei sticks, use raw (multiple) aloeswoods with some 100% natural oils to give a Kyara-like scent, with the amber accords, and sweet, floral notes.
Japanese incense, especially Shoyeido, Tennendo, Seijudo, Kunmeido, Gyokushodo, premium range Nippon Kodo and Minorien, are all artisanal range sticks. Some of these companies have been around of hundreds of years, like Shoyeido around 300 (and they would produce and provide incense for the emperors and nobles of Japan) years and Tennendo around 400 years.
If you also want some single ingredient oud and sandalwood incense that is made to an artisanal quality, KyaraShrine has amazing incenses!!! I would really check her out on Etsy. She is Japanese and very connected to a few houses.