Book of Water

The Book of Water contains the ancient wisdom of Shinsei. It is only described as a thick bundle with the symbol for Water on the front.

Enlightenment Challenge
The challenge for the Book of Water was

"The general who can lead armies from one end of the Empire to the other in a single night..."

Doji Jun'ai completed this challenge when after hearing about Kakita Tsuken's brave defense of Fujita Mura, she raised an army overnight to stand against the main Mantis Clan army led by Yoritomo Naizen. Although Tsuken had honor bound one Mantis army to leave Fujita Mura unmolested, the second army behind them had no such restrictions, so Tsuken's brave sacrifice would have been wasted.

Originally, Doji Jun'ai had been ordered by her superiors not to interfere in the war between the Phoenix Clan and Mantis Clan despite the Crane Clan being allies with the Phoenix. Tsuken's bravery inspired her to defy her orders and both their actions inspired many more to flock to her banner to bolster her meager troops, from peasants to magistrates, and even an Ox Clan diplomat. In the end, her army was able to stand against Yoritomo Naizen's and Fujita Mura was saved once again.

Rosoku explains this challenge's riddle at the end, saying

“There are two sorts of samurai in this Empire. At one end, those who use their gifts only to gain selfish glory. They will stand blindly to one side, and let war consume the innocent, claiming they were powerless to act. At the other, there are those who will always fight, regardless of the odds, even when there is no hope. And the general who can lead armies from one end of the Empire to the other in a single night, shall keep the Book of Water.”