Adult Yamamoto using Shinotsaku Ame
The 8th form of Shigure Soen Ryu: Shinotsuku Ame 篠突く雨 (Pelting Rain) - Offensive. Yamamoto uses the blade of the sword to cut around the bearer.
This attack was originally created by Yamamoto's father while saving his friend in the middle of a Typhoon. While training Yamamoto also mentioned that it was the easiest of the eight forms for him to learn and as a result uses it far more than any other in the series. Yamamoto first used it during the Rain Ring Battle against Squalo, who had already learned the other seven styles from another user of Shigure Souen Ryu. However because the eighth form that had been passed on by Yamamoto's farther was different, Yamamoto was able to successfully strike Squalo for the first time. In the future Yamamoto improved Shinotsuku Ame, using it to surround himself in Rain Flames.