The previous few weeks had shaken Iwan's confidence in Tokugawa's ability to unite Japan. Tokugawa's lords seemed to have a lot of trouble making it to the front lines, and they had actually lost a lot of territory to Mori. Trying to figure out what was wrong, Iwan spent some time reviewing what he knew about Tokugawa's vassals. It turned out that they more or less fell into three categories: loyal, longstanding vassals who had been rewarded with numerous fiefs, rebellious lords with no holdings of their own, and one single newcomer, who seemed to be willing to give his new lord a chance.
Tokugawas empire was having trouble holding its own because it had grown too big. The loyal lords had huge armies and crushed all resistance easily, but took many days to reach the frontline once they were done supervising their numerous fiefs. The newcomers were attracted to the many available fiefs, but Tokugawa was taking his time with assigning them, which was making him decidedly unpopular. Some of the landless vassals would spend their time on the front lines, and even take the cities and castles weakened by Iwan. But Tokugawa was unwilling to assign fortified fiefs to people who disliked him intensely, so he would favor his long term vassals. As a result, he was quickly losing the most active of his new vassals.
There was little Iwan could do apart from destroying Mori's armies, and repeatedly assaulting their holdings. It was slow going, but as Mori was beset on all sides, and Tokugawa wasn't really fighting anyone else, he was hopeful. After all, with so many garrisons reduced to single digits, Tokugawa's lords were bound to capture some, once they actually made it to the fight.
Iwan spent a couple of weeks in Mori territory, hunting down any lord who ventured outside their walls. He did not want to give Mori a chance to fight back, so he did not even take the time to visit any cities but theirs. He was infamous, and the gate guards knew him on sight, so he became pretty good at just battering his way in and losing himself into the crowd. He tried to rescue Mori's enemies, every time he learned one was in jail, but he felt he did not have the time for proper preparations, so very often he had to leave them behind.
By the time Tokugawa's truce with Chosokabe was about to expire, Mori had lost 17 population centers. Tokugawa still only had two lords for every three of Mori's, but at least new hopeful vassals were replacing the ones who defected or were indicted for treason. Iwan hoped that Tokugawa would refrain himself from attacking Chosokabe once the truce ended, but he didn't really expect it to happen.
And indeed, on the 342nd day, Tokugawa resumed hostilities with Chosokabe. At least, Mori had been greatly diminished, so Iwan switched his efforts towards facilitating Chosokabe's defeat. With one city and two castles, they might be easy to eliminate... but it all depended on how quickly Tokugawas loyal lords would bring their huge and unwieldy armies to bear.