Rin is Yuugo's childhood friend. Rin is the Synchro Dimensional counterpart of Yuzu Hiragi (Standard Dimension), Serena (Fusion Dimension) and Ruri (Xyz Dimension). According to Leo Akaba, Rin is crucial to his plans. She was kidnapped by Yuuri sometime in the past. (Source: Yu-Gi-Oh! Wikia, edited)