The Bidirectional Series is a group of songs featuring Luo Tianyi, YANHE, and Yuezheng Ling, who initially borrowed YANHE's voicebank due to not receiving her own when the series began. It tells the tale of Tianyi and YANHE's love for each other, with Ling having a one-sided romantic relationship with YANHE. As a result, a war was created between the three.