The Shisui (止水 Stopping Water) is a white-wood Shirasaya (a katana without a tsuba/guard) wielded by Motoko Aoyama throughout Love Hina.
Its design is typical of the swords found in the Shinmei-ryu School of Swordsmanship, possessing two bells tied with red string at the base of the grip.
Originally Tsuruko Aoyama’s favoured sword, she passed the Shisui on to her sister, Motoko, as a farewell gift before leaving to embark on missions for the school.
Motoko kept the Shisui as her primary weapon, training with it and taking it with her when she moved to the Hinata House. However, when Tsuruko arrived at the dormitory to bring Motoko back home, Motoko attempted to dissuade her sister by lying about being engaged to marry and, having discovered the lie, Tsuruko defeated Motoko in a duel and broke the Shisui’s blade as punishment, and with it, Motoko’s spirit was also broken.
Though Motoko eventually recovered from the ordeal, having found and obtained the Hina Blade to use as her new primary weapon, it is unknown whether the Shisui was ever reforged, though a Shinmei-ryu blade similar to the Shisui is tucked in Motoko’s belt during the incident surrounding Kanako Urashima’s arrival to Hinata House (Ch95).