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.
In this series, the story repeats itself over and over, each with different endings. Every choice the characters make decides the ending. However, there is implication in 单向苏醒 (Dānxiàng Sūxǐng) that YANHE was the one who keeps resetting the story.
In August 2015, an album called Shuāngxiàng·Lúnhuí yǔ Xìngfú (双向·轮回与幸福) was released and contains all of the songs in the series. All songs were remastered and Ling's vocals were used in the songs that were intended for her originally. It also contained a brand new track which is the final ninth song of the series.
Two characters (Tianyi and YANHE) have an unspoken love for each other, but neither of them knew how one felt about the other. Their love spirals out of control as YANHE pretended to date another girl (Ling), in order to gain attention from Tianyi. He succeeded in receiving her attention, but it came with the price of his life as Tianyi murders him instead.
A rearranged version of the first song, but with a different ending. In the end, rather than Tianyi killing YANHE, she spared his life when he confessed how much he loved her and they finally overcame their own boundaries, following their hearts.
Ling is deeply in love with YANHE, but she knows that he actually loves Tianyi and not her. She is also aware that Tianyi loves him back, so her love for YANHE grew into pure hatred. As a result, she plotted and planned traps for the two and made it seem like they hated each other, which causes the pair to become desperate for their love.
Another alternative ending to the first song, where Ling realizes her actions could hurt YANHE and decided to put an end to the fighting. She confronts Tianyi before she kills him and confessed that the plots were her fault. Ling leaves, allowing the two to be together.
Ling was murdered by Tianyi out of jealousy and her head was sent to YANHE as a plot to imprison him, but was foiled when the police arrests Tianyi instead. However, this traumatizes YANHE and caused him to be sent to an asylum as he started becoming insane from the experience.
The character song of Tianyi. This song tells the story of her dark secret and the reasoning behind her desire to commit murder. It was revealed that Tianyi actually has two different personalities, a light side and a dark side, where dark side acts as a sort of guardian to the other. Once the light side became brokenhearted over YANHE, it gave in to the dark side, which takes over and decided to murder YANHE as revenge.
The character song of Ling. In the past, Ling grew up in a happy family and she had many friends. However, her parents divorces after her father was caught cheating and Ling loses faith in love and her friends. When she met YANHE, her belief in love was renewed and she fell head over heels for him. But when she found out that he actually loved Tianyi and was only using Ling to gain attention, Ling loses her faith in love for good and decided to destroy YANHE and Tianyi's feelings for each other, which leads the events taking place in the third song, 单向宣战 (Dānxiàng Xuānzhàn).
The followup of 双向监禁 (Shuāngxiàng Jiānjìn). It is also the character song for YANHE. He is stuck in the asylum and regrets that he never told Tianyi his feelings for her. He decides to confess his love in order to reverse the events that happened, but she kills him anyways, so that "they" (her dual personalities) would not lose him again.