A yari forged by Masazane Fujiwara in the Muramasa tradition. It's one of Japan's Three Great Spears, famous for a legend about its ridiculous sharpness—supposedly a dragonfly landed on the blade and got cut clean in half, which is where the name comes from.
The character's main deal is being genuinely honest and straightforward, which makes him reliable for missions during the Sengoku period. He tends to get sent out into the thick of things, which tracks given his no-nonsense personality.
Content compiled by AnimeList.moe from publicly available sources.