Dōshin 同心
Low-ranking Edo-period officials who did much of the shogunate's practical policing, patrolling the city, investigating and arresting suspects, and training in the arrest rope.
Dōshin were low-ranking retainers of the Tokugawa shogunate. Kotobank’s dictionaries place the best-known of them, the town dōshin, under Edo’s town magistrates (machi-bugyō) and their senior officers, the yoriki. Their work was policing and administration: patrol units moved through the city, investigated incidents and detained suspects, carrying a jitte truncheon with a red tassel. Dōshin also paid private assistants, the okappiki or meakashi, who were not official staff and could not arrest anyone without a dōshin’s order.
Their link to rope comes through hayanawa, the quick arrest rope. Kotobank’s entry on it says dōshin were reputed to practice its complex bindings until they had mastered them, alongside the longer honnawa used once a charge was fixed.