manga writers ofter have to ditch or skip entire story elements that they wanted to press due to the magazine publication and volume book page limitations, editors suggesting that it is not interesting and slows down the plot, and pressure from the publishers to get to a certain point by a certain time. the data books are an excellent way clear up some things left behind, not fully explained, or forced to retcon. its really a method to earn more money, and kishi is hardly the only manga creator to write data books. they are tools that lots of creators use to inform their community of readers.Originally Posted by Uchiha Barles