Kotoku

Kotoku is the Ancestral Yari of the Daidoji family. It was forged by Doji Yasurugi and was as powerful as the other swords Yasurugi crafted. Shortly after its creation, Yasurugi managed to defeat six of his skill kinsman simultaneously. The yari was given to Doji Hayaku whne he retrieved Yasurugi's blade from the Shadowlands shortly after the first Day of Thunder, and Kotoku became thereafter the ancestral weapon of the Daidoji family. It was lost when Daidoji Masashigi wielded it against a great oni and was swept into Earthquake Fish Bay at the Battle of Tidal Landbridge. It was never recovered from the Bay.

Major References
Magic of Rokugan, p. 66.