Bamboo breathing tubes are two-foot-long cylindrical objects made of bamboo, designed to be watertight for underwater breathing. They were discovered buried among reeds along the shore, with scrape marks on nearby rocks indicating their use in a waterborne infiltration. The tubes were likely utilized by assailants to hide in the reeds until after midnight, allowing them to approach the castle undetected.
During the investigation, Bayushi Monban and Kakita Kazumi found the breathing tubes while searching the island's shorelines for signs of infiltration. Kakita Kazumi hypothesized that the assailants had slipped off a high-traffic boat, hidden in the reeds using the tubes, and then approached the castle. Kazumi later applied a numbing poison inside the recovered breathing tubes and, with Monban's assistance, replaced and concealed them to appear undisturbed.
In a subsequent investigation, a different set of breathing tubes, known as Snapped Reins Breathing Tubes, was discovered hidden under shoreline rocks. These tubes, crafted from repurposed snapped reins, were similarly designed for covert aquatic approaches. Kakita Kazumi reported their discovery while addressing guests about recent intrusions and a poisoning incident, linking them to the ongoing inquiry into suspicious activities involving the Crane couple, Doji Masato and Doji Miho. The presence of these tubes further indicated a potential threat in the investigation surrounding the poisoning of Shiba Midori, highlighting their significance in the broader context of the unfolding events.