|Title||Rondine di Pioggia ver. Vongola|
|Cambio Forma||Asari Ugetsu's Four Irregular Swords|
|Manga Debut||Chapter 240|
|Anime Debut||Episode 75|
Yamamoto's exclusive Box Weapon was created by remodeling a Rain-attribute Rain Swallow. It is imbued with Vongola's latest technology. Along with the Rain Dog, this is one of the two Box Animals that make up Yamamoto's Vongola Box. Yamamoto has named it "Kojirou".
Its basic performance is the same as the normal Rondine di Pioggia, but it can combine with Yamamoto's Shigure Kintoki through Cambio Forma to change its shape into the longsword-style weapon that was used by the First Rain Guardian. Also, as shown during the Choice Battle, it is capable of raining down Flames with the Tranquility effect over a large area.
- Cambio Forma: Asari Ugetsu's Four Irregular Swords - Composed of the longsword created by the fusion between Kojirou and the Shigure Kintoki along with the three short-swords provided by Jirou. The longsword's hilt possesses wings-like decorations and a single jewel with the Roman Numeral "I" in the middle. During the rematch between Yamamoto and Genkishi, the Rain Flames released by it were able to slow down the enemy's own Flame-based attacks to the point they seemed to not be moving at all.
- It takes its name from the sword-master famous for the "Tsubame Gaeshi" (lit. Swallow Reversal) sword technique.
- On another note, the swordman Kojirou was also known for his skill with the nodachi Japanese longsword. His personal blade was called Monohoshizao (roughly Laundry-Drying Pole).
- If you remove "Ko" from the name Kojirou, you get "Jirou," the name of the other half of the Rain Vongola Box.