Who Are the Toku-no-ichi / Matsu-no-ichi?
The two travelers who dropped Kita in the river
Zato
Toku-no-ichi and Matsu-no-ichi are the two zato who try to cross a river in Book 3 of Tokaidochu Hizakurige (Shank's Mare). Zato is a term that comes from a rank in an Edo-period organization of blind people, and it was also used for people who earned their living through the arts or other trades.
The two are crossing by carrying each other on their backs. Seeing this, Kitahachi decides to get across for free and silently climbs onto a back, but he is noticed partway over and dropped into the river, soaked to the skin. It is a story of a cunning man who underestimates others and pays for his own behavior.
The butt of the joke in this scene is not the zato but Kitahachi, the cheat. The manga does not make blindness the source of its humor and portrays the two as quick-witted people who are a step ahead of him.