I own one of these journals and can say that this is authentic Tomoe River paper and it is one of the most high-quality notebooks I have ever used.

Japanese Tomoe River paper is a favorite among those who love to write and are particular about quality. It's renowned for being incredibly thin with a velvety smooth texture. Performs amazingly well with fountain pens and ink pens. "Tomoe River FP" paper is Tomoe's top-of-the-line paper. It is the highest quality paper available and specially designed for fountain pen users.