From: the Intro to Basho's Narrow Road by Hiroaki Sato
Was Bashō a Ninja?
"When a renga master traveled, it was important to have an array of literary-minded merchants, samurai, or other people of means lined up along the way. People who were willing to accomodate the visiting poet for the pleasure of taking part in a session or two of renga composition. When such people were not available, as apparently happened during parts of Bashō's travels to the north, the itinerant poet could be reduced to an itinerant pauper.
Here, because several aspects of this famed journey, such as expenses, remain a mystery, I might as well touch on a speculation (not altogether implausible) that Bashō might have served as a ninja during his travels to the north.
Bashō was from a former warrior-class family in Iga, Mino, a famous breeding ground for ninja, who were often employed as spies. Just about the time Bashō set out to the north, there was a quiet dispute between an agent of the Tokugawa shogunate and Date Tsunamura (1659-1719), concerning the renovation of the Nikkō shrine. The Nikkō, which Bashō and Sora planned to visit early on in their journey, was the resting place of the founder of the Tokugawa shogunate. The Date family was assigned to renovate this shrine, and the cost was expected to be ruinous . . . The shogunate may have planned to dispatch a secret agent to look into the matter.
There are, in addition, some circumstances that cannot be fully explained. Bashō originally had in mind a different traveling companion, but switched to Sora at the last minute. Also, Sora apparently did not leave Edo at the same time Bashō did.
To our disappointment perhaps, the scholar, Muramatsu Tomotsugu, after an exhaustive documentary investigation, had to conclude that Sora, not Bashō, might have been given some duties to carry out by the government, but there probably is nothing more to the story.
The speculation that Bashō may have been a ninja arose partly because of a diary that Sora kept during the journey, which was not published until as late as 1943. Such theorization aside, though, this perfunctory recording of day-to-day occurrences indicates that Bashō's composition was not a straight 'travel account.' Bashō reshuffled dates, concocted some poems for Sora, created impressions contrary to what actually happened, and otherwise fabricated for literary effect."