A Touken Ranbu character. A tantou crafted by Awataguchi, and thus one of the many Toushirou brothers.
In 1493, Hatakeyama Masanaga tried to commit hara-kiri using this dagger, but he couldn't cut deep into his flesh. He got angry and threw the dagger, and then the dagger pierced directly through a yagen (a stone mill for medicinal herbs). The dagger gained the reputation for never damaging its master but sharp. That's responsible for its name. He was also owned by Oda Nobunaga at one point. It's said that Yagen was burned down at the Honnō-ji Incident with Nobunaga.
Known for being very mature and reliable, and having a very deep voice despite his youthful appearance. Of course, artists tend to portray him as a precocious kid. Either that, or he's presented as a reliable big brother for the other Awataguchi school tantous when Ichigo is away, as he's the only one of them in-game that's been used in combat prior to personification. For this reason he's known as "Aniki" outside of game.
