|Title||Rondine di Pioggia|
|Manga Debut||Chapter 140|
|Anime Debut||Episode 75|
Kojirou is a Rain Attribute Box Weapon that is clad in Rain Flames. The choice of a swallow for Yamamoto's Box Animal most likely draws from the fact that the kanji that represents the bird is part of his fighting style's name, the Shigure Soen Ryu.
Because the Tranquility effect of the Rain Flames weakens the opponent's Flames, it is effective in both offense and defense. As shown during the battle with Nosaru, its Flames are strong enough to actually extinguish enemy Flames and also have other uses such as providing camouflage. Furthermore, it can send rain by using the moisture in the atmosphere. It is capable of high-speed flight, and, because all its abilities but strength are high, it is a Box Weapon that conceals exceedingly advanced three-dimensional fighting abilities.