I actually think there’s going to be a time lapse between book 3 and 4. The emperor said that after his wedding there will be one year of peace and prosperity.
It seems to me that’s what we achieved throughout the first three books. The yakuza are defeated, the rebels crushed and a power hungry fox demon is slain. Besides, Hatch now commands an enormous samurai army that is loyal to the emperor.
Maybe we’ll jump ahead for when things restart falling apart? At the end of that one year, new threats might arise against the empire and, more importantly, its people.
Whatcha you guys think?