Momotaros is one of Ryotaro Nogami's main Imagin allies, and a member of the four Taros aboard the DenLiner. When possessing Ryotaro or by himself, he can transform into Kamen Rider Den-O's Sword Form (ソードフォーム), later becoming the sole representative of the Den-O series in Ryotaro's absence.

(Source: Kamen Rider Wiki)