When QUARTET NIGHT is chosen to perform as the Triple S Opening Artist, they decline the opportunity after STARISH and HEAVENS give equally compelling performances. Raging Otori and Shining Saotome propose another musical showdown to determine the opening artist between the three groups in which all three of them must sing songs written by Haruka! Who will win the decisive concert and the honor of performing at the Triple S?

The members of STARISH and HEAVENS are shocked to learn they will be singing duets with members from the other group to prepare for the decisive concert. Meanwhile, QUARTET NIGHT appears to be experiencing some discord of its own.

The second group of the Duet Project is Syo of STARISH and Yamato of HEAVENS. Syo is excited to sing a duet with Hyuga Ryuya's younger brother, but a powerful rivalry with his older brother surges through Yamato's heart.

The third duo of the Duet Project are Cecil of STARISH and Shion of HEAVENS. Trying to follow up on Tokiya and Syo's success, Cecil aggressively approaches the project, but Shion closes off his heart more and more as though in response to Cecil's passion.

The fourth duo of the Duet Project are Ren of STARISH and Van of HEAVENS who are also slated to play rivals in a TV drama. When Van begins aggressively pursuing Haruka, Ren heads straight into battle with his own passionate feelings hidden in his heart.

At their meeting for the Duet Project, Nagi's casual remark causes a sudden change in Natsuki's positive behavior. From Natsuki's words and past videos, Nagi realizes his secret...

Due to their inborn earnestness and similar backgrounds, Masato and Kira both sense how compatible they are with one another. However, while work on the song is going smoothly, Kira fears something is lacking. Meanwhile, Masato receives word from his family...

The theme of Otoya and Eiichi's song is a "soul-shaking song." When Eiichi explains to Otoya that he must face his true self that exists deep inside his heart to do so, he stoically engages in writing the lyrics. However, gradually he becomes less and less like himself.

Leaving behind a completed duet, Otoya disappears. Having been exposed to a side of Otoya they'd never known before through his voice, as the members of STARISH search for clues that will lead them to Otoya, they arrive at the truth behind his personal history.

After reuniting in the sunflower field, STARISH successfully makes it to their live broadcast while becoming the talk of the town. With the Duet Project finished, STARISH and HEAVENS are set to start working towards the Decisive Concert. However, a plot to drive them towards despair is approaching.

The emotions and hoeps of STARISH, QUARTET NIGHT, and HEAVENS are illuminated by a morning sun rising in a clear sky. As Haruka prays for similar things, the Decisive Concert is about to begin.

QUARTET NIGHT and HEAVENS have finished their own brilliant performances, which leaves only STARISH. Will their performance match the passion of the other two groups? Who will be chosen to perform as the Triple S opening artist?