Hi! Treasure rate has always been a random chance, but players have determined through their own experience and data that there is a threshold one needs to meet in order to get either a rare or super rare. At the moment, the treasures only guarantees that you get an uncommon every "Draw Ten". A little luck is involved in pulling for treasures. The best way to get exactly what you need is to purchase the fragments at a discount in events. Treasure draws have always been a random chance, but getting fragments from events are guaranteed.

We are the English version of Naruto Online and therefore we are still a little bit different from the China version. I hope that helps!

~Jib