"Stand by U" is South Korean pop group Tohoshinki's twenty-eighth Japanese language single. "Stand by U" was released on July 1, 2009 by their label Rhythm Zone and was released in two formats: CD and CD+DVD. The track serves as the final single promoted by the group as a five-piece, following which legal troubles caused the group to go on an extended hiatus.
Upon the release of the single in Japan, it took the number two spot on the Oricon daily chart selling over 94,800 copies. On July 5, 2009 daily chart the single peaked at the number-one spot selling nearly 29,300 copies. On the issue date of July 13, 2009, "Stand by U" debuted at number two on the Oricon weekly chart behind popboy bandArashi's "Everything"; selling a little more than 182,060 copies.
Like their twenty-third Japanese single, "Dōshite Kimi o Suki ni Natte Shimattandarō?", two music videos were shot for "Stand by U": drama version and version with Tohoshinki's members. Both videos were shot by Hideaki Sunaga (須永秀明,Sunaga Hideaki) and the video features the members in a hotel. As the song was used as the theme song for Japanese mobile drama Sweet Room, the music video features the characters of the first story Last Love starring Narimiya Hiroki as the male lead and Yukari Shiomi as the female lead.
On June 20, 2009, Tohoshinki appeared on Music Fair and performed "Stand by U" as well as "Sky". They also appeared on other shows such as NHKSave the Future 2009, Music Station and Music Japan, performing "Stand by U".