A question about when to take the last level on the last book:
The players begin 13 level and go through the Well of Demons. When they get out they are 14. And then they go into the palace. But the book says that before they confront with the Jade Regent they are 15 level. When do they actually get the last level in the castle and how? I mean, to gain a level you need to rest. And how is it gonna work? We go to the palace, clear 2 floors, leave, rest, level up and then we continue? And if that is the answer, what happens to the battle that started outside the city with the armies?
Option 1: Waive the rest time. Simply have the spirits of the honored ancestor emperors, and the guardian kami, and the ancestral weapons etc. allow the PCs to gain a level when they first sight the Jade Throne. If you feel generous (and you might), have them also restore the party to full HP and spells, except for those actually still in effect.
Option 2: The forces present in the Castle are all the forces the jade regent has remaining. This option allows the palace to be whittled down piece by piece like a more typical dungeon. The battle of armies outside takes several days to resolve. (Note though that for each day in the capital the PCs lose one 'Rebellion Point' so if they take a while this can transform a victory into a loss)