Theory: What Aoteru and Kaku's true plan is to intentionally convince Taira Denki not to deploy troops for conquering Seii to avoid Yamato's defeat

Seii's Commander-in-Chief, Ōga, said she plans to destroy Yamato's army through attrition as she lures it into the heartland and burns the crops over the course of Seii's cold winter, so Aoteru's likely foreseen her plan and will leverage that to stress to Taira Denki that deploying to conquer Seii would result in their army facing certain defeat, hoping Denki will allow him to conduct a mission in which he withdraws as much of Yamato's army from Seii's territory. In the past, Napoleon suffered a huge defeat to the Russians in the manner Ōga's proposed here, which led to the end of his rule as the Emperor of France in time. This is almost certainly Aoteru's real plan to save Ryumon and Kaku and even Denki's son so that the pair don't get executed for having botched the mission.

He probably won't cite Napoleon as I doubt a mug like Denki even knows who he was, but he'll surely bring up a man in Japanese history, whether real history or this alternate history, to draw attention to a full deploying of Yamato's remaining troops being a grim idea exactly 'cause Ōga intends to pare down their army over a long winter with Seii's invasion of Yamato being a trojan horse.

I imagine Aoteru will bring up Moriyama's betrayal and (Incoming? or perhaps it has already happened) escape and the glut of soldiers charged to look after him in his exile to boost that Ryumon and Kaku knew of how Seii operatives had been festering treason and drawing them into a war of attrition, and that's the reason they didn't cross the river to follow his son, Tonotsugu, into Hanazawa, a trap where 30,000 troops are sitting stranded.

Given Aoteru's commoner origins, I expect he'll propose that Tsune lead the troops since he comes from a prestigious clan, and Aoteru will stake his own life on this mission's success in saving Tonotsugu, and that'll be what convinces Denki to permit this mission as he wouldn't want to project weakness to the populace or his followers for withdrawing following Yamato having been invaded.