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.

He has [[short hair|short]] [[black hair]] and [[purple eyes]]. His standard outfit is a [[military uniform]], a [[necktie]] and [[black gloves]]. For his Internal Affairs outfit, he wears [[glasses]], a [[lab coat]] and [[suspenders]]. For both outfits he wears [[shorts]] and [[black socks|black]] [[kneehighs]].

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 hitofuri|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.
薬研藤四郎