Koshu-kaido is the northwestern route Toranaga proposes taking toward Kyoto when the coastal approach appears too costly. In the military debate over his escape from Osaka, the road offers a possible way around forces controlling the coast—but not a safe passage: Zataki’s defection places another enemy barrier across it, turning the route into a test of terrain, allegiance, and available choices.

Strategic Route

Toranaga plans to move northwest along Koshu-kaido and then strike down toward Kyoto, avoiding the coastal lands. Yabu contrasts this plan with the Tokaido, where Ikawa Jikkyu’s forces obstruct a long stretch and further strongholds held by Ishido’s side lie beyond. The road matters as an alternative line of movement, not as an open corridor: the choice of route can change which hostile forces Toranaga must confront, but it cannot remove the danger.

The Shinano Obstacle

The plan becomes more precarious when word arrives that Zataki has joined the enemy. His province lies across Koshu-kaido, so Toranaga would have to fight through all of Shinano. Yabu stresses that the province is mountainous and difficult, and that Zataki’s men are fiercely loyal; he expects Toranaga’s force to be cut to pieces there. Toranaga acknowledges the risk but maintains that the northern approach is his only chance, since too many enemies control the coastal road.

Narrative Significance

Koshu-kaido embodies the narrowing of Toranaga’s options. The proposed detour first appears to offer a way around the coastal defenses, but Zataki’s change of allegiance turns the route itself into a threatened passage. Its strategic importance lies in that reversal: geography does not simply direct the campaign but makes political loyalties physically consequential, as a hostile province can close a road as effectively as an army.