You can acquire this once you win the match in League 2.
The Gold that you can get from Exclusive Books will be 10x more than the usual Books.
Once you purchase Prime, should the number of Books set on the empty slots at the time of League Match Victory matches the ones below, it will become Prime Member Exclusive Books.
・3-Day Prime Membership ... 3rd Book
・7-Day Prime Membership ... 1st Book and 11th Book
※When you purchase mutiple Primes at the same time, please be guided that it will not follow the conditions above. The Prime Member Exclusive Books will appear on the 3rd Book within 14 Books.