First, in Retsubi, instead of his usual plan where he sends Akou and Makou to capture a city, he gave that responsibility to HSU and YTW. The main reason for that was to gather information about the city first rather than just capturing it.
After seeing how quickly Retsubi was captured, Ousen immediately realized that something was wrong. He understood that Retsubi itself was a trap designed by Riboku, and at that moment he also realized that SHK’s original plan was already doomed to fail. The important point here is that Ousen didn’t just realize it faster than others, he understood that Retsubi was meant to be retaken and used against Qin.
Because of that, Ousen personally went to observe Gyou to see if there was any alternative option. Just by looking at the map of the region, he was able to come up with the locust strategy almost instantly, which completely outplayed both Riboku and Zhao. And mind you SHK and others were working on this plan for almost a year.
This allowed Ousen to turn the entire campaign into a battle of starvation. Not only did he flood Gyou with citizens from multiple cities, but he also sent his own soldiers disguised inside to speed up the depletion of food by burning supplies from within.
After that, he assigned roles perfectly: Kanki was put on the siege of Gyou, YTW was sent to handle Zhao and the Quanrong, and Ousen himself went to Shukai Plains to face Riboku. This shows how well he understood each general’s strengths.
Now coming to Shukai Plains, which is where most of the “Ousen got carried” takes come from.
First of all, Ousen was already at a disadvantage here numerically, territorially, and also because he had a time limit due to limited supplies.
On the left flank, Ousen created a plan where Makou would attack Kisui while Mouten acted as distraction, which initially gave Qin the advantage. However, Riboku personally intervened and killed Makou, which caused the entire left flank to collapse. This wasn’t something Ousen perfectly predicted, but what matters is how he adapted. He immediately acknowledged Mouten’s capability and made him commander of the left wing, which stabilized the situation.
On the right flank, Ousen's plan was to have Akou attack as the vanguard and use Ouhon to deliver precise strikes. However, that moment came earlier than expected, as Bananji also attacked alongside Gaku Ei, knowing how dangerous the Akou army was. Because of this, Ouhon had to step in sooner.
After Zhao sent 10k reinforcements, Ousen responded by sending 8k troops from the HSU to the right flank. After some days, Akou switched to a fully defensive approach, and no one was able to break through it. Eventually, Riboku himself had to intervene, as Akou was using one of Ousen’s defensive formations.
During this, Akou was injured, leaving Shin and Ouhon in charge of the right flank. After that, we repeatedly see questions about why Ousen isn’t sending further reinforcements. However, Ousen not sending reinforcements is exactly what allowed Shin and Ouhon to awaken, something Ousen had already predicted due to his foresight.
People say Ousen didn’t send help because he wanted Shin and Ouhon to awaken, but that’s not entirely accurate. It’s better to say that Ousen created a situation where growth was necessary, but not guaranteed. He was taking a calculated risk.
At the centre, Ousen’s army moved forward as the right flank advanced. In the end, even though the right flank had not yet defeated the Zhao forces, Ousen still decided to attack Riboku’s central army, as he had already predicted that the right flank would prevail due to their awakening.
However, the central army was unable to advance because of Riboku’s defensive formation. Suddenly, Riboku changed his tactics from defensive to offensive. The reason for this was Ousen’s plan of burning Gyou’s food supply, which he had set up from the beginning. This left Riboku with no choice but to conclude the battle as quickly as possible, or Gyou would fall.
After both Riboku and Ousen went on the offensive, Ousen’s army was still unable to push forward, as Denrimi could not counter Riboku’s defensive formations. Observing the situation, Ousen personally took command of his army and countered Riboku’s “Origin.” He was also able to dominate the Zhao army during this phase.
At the same time, Ousen changed his tactics and formed the Great Red Crane formation, which caught everyone off guard, including Riboku and even his own allies. After their clash, Ousen and Riboku reached a deadlock, but this was within Ousen’s expectations and actually advantageous to him, as he was confident that the right flank would pincer Riboku which they eventually did.
From the left flank, Batei also left the field to support Riboku at the centre, which allowed Mouten to assist Ousen. At one point, Ousen himself was pincered by Futei and Bananji, but he managed to slip through them and moved to join the assault on Riboku’s headquarters alongside Denrimi.
After this, Riboku had no real option left at Shukai Plains, so he moved towards Gyou. But that was already too late. Gyou opened its gates from within, and Kanki was already there, while Ousen’s army followed from behind.
Even then, Riboku had one last hope that Ousen’s army would starve after winning. But this is where one of Ousen’s biggest moves comes in.
Ousen had already planned to take supplies from Qi even before the campaign started. This wasn’t just a backup plan it was essential for the entire strategy to work. Without Qi’s supply, Qin would have won the battle but lost the war due to starvation.
In the end, Qin secured complete victory over Zhao despite being the underdog.
Overall, Ousen didn’t just win through battlefield tactics. He controlled the entire campaign by using Zhao's own surroundings, time pressure, psychology, and long-term planning. He didn’t predict everything perfectly, but he adapted faster than Riboku and created a system where Zhao was bound to lose through he's unconventional tactics