Honshu is presented as Japan’s main island, distinct from the strongly Catholic Kyushu and embedded in a wider geography of islands, coastal routes, and difficult sea passages. Its importance lies not only in its place within the archipelago but also in the contrast between its sparse Christian institutions and the religious and commercial influence concentrated farther south.

Place within the archipelago

In Rodrigues’s account, Japan consists of three large islands—Kyushu, Shikoku, and Honshu—and thousands of smaller ones, with Hokkaido far to the north. His description makes Honshu the central point of comparison in a fragmented island geography rather than an isolated landmass. The distinction matters to Blackthorne, who is trying to understand the scale and political reach of the society in which he has arrived.

Rodrigues’s explanation is delivered while he is injured and speaking feverishly, so his sweeping judgments about Japan are his own, not a neutral geographical description. His account nevertheless conveys the archipelago’s scale and the strategic importance of understanding its separate regions.

A different religious landscape from Kyushu

Rodrigues describes Kyushu as the center of Catholic strength: hundreds of thousands of converts, most of the island’s daimyos converted, and Nagasaki under Jesuit control, with its trade passing through the city. Against that concentration, he says that Honshu has only a few churches. The contrast places Honshu within a religious landscape where Christian influence is unevenly distributed, not a uniform presence across Japan.

His account also links this imbalance to political uncertainty. He recounts that The Taikō’s expulsion orders were not consistently enforced after their announcement, but that twenty-six missionaries were later martyred at Nagasaki. These events are reported by Rodrigues as part of his explanation of Japan’s changing Christian fortunes; they establish the perilous background against which the comparatively small Christian presence on Honshu is understood.

Coastlines, routes, and navigational knowledge

The waters around Japan are difficult to navigate with the charts available to European pilots. Blackthorne’s knowledge identifies the central problem: existing charts are vague, and longitude cannot be fixed. A rutter—the accumulated observations of a pilot who has already sailed a route—can compensate with recorded compass courses, depths, seabed, winds, currents, storms, anchorages, and hazards. Yet such books may contain copying errors or deliberate falsehoods, and a pilot cannot be certain of their accuracy until he has sailed the route himself.

A passage along the east coast of the Izu Peninsula illustrates the choices these waters impose. The galley first runs south with the help of a large sail; off Cape Ito, Rodrigues turns west-southwest across open water toward Cape Shinto, roughly two hundred miles away. Hugging the coast would be safer but slower, while the open-sea course serves the urgent task of carrying Toranaga to Anjiro and back quickly. The route shows how coastal geography and navigational judgment become immediate political considerations.

Maritime exposure and narrative significance

The book also sets coastal movement against the danger posed by armed European ships in unfamiliar or hostile harbors. Blackthorne recognizes the standard precaution of moving a frigate offshore into deep water when danger threatens from land: its guns are prepared, armed men watch from the rigging, and stern chasers can cover an approaching vessel. In a later chase near cliffs and a harbor mouth, the galley’s freedom to maneuver is set against the frigate’s greater speed and its need to tack into the wind. The narrow sea room leaves little margin between a successful passage and disaster.

Honshu therefore belongs to a setting where land, harbor, and open water are inseparable from power. The island’s limited Christian infrastructure distinguishes it from Kyushu, while the larger archipelago’s uncertain routes and contested anchorages determine who can travel, pursue, or escape. For Blackthorne, geography is not a static map: it is knowledge tested at sea, with consequences for the political struggles unfolding ashore.