Misaki Takahashi and Akihiko "Usagi" Usami have been cohabiting for three years, and their bond has been developing without major issues. But every strong relationship encounters difficulties, and theirs is only starting to face them. A fresh competitor appears, causing Usagi to fret over whether Misaki's affections still lie with him.
Meanwhile, Ryuuichirou Isaka has long enjoyed meddling in Misaki and Usagi's romantic affairs, yet his own relationship is far from untroubled. He and his secretary Kaoru Asahina have been together for several years, but Asahina insists on maintaining a clear boundary between work and personal life, which frequently creates turbulence between them.
Regarding Nowaki Kusama and Hiroki Kamijou, as their professional lives begin to flourish, they increasingly find themselves with little time together. The dwindling moments they share allow uncertainty and self-doubt to edge into their connection. In contrast, the seventeen-year age difference between Shinobu Takatsuki and You Miyagi has always posed a challenge, yet as they deepen their understanding of one another, their past self-awareness gradually diminishes.
The cherished pairs from Junjou Romantica, Junjou Egoist, and Junjou Terrorist return once more, joined by a fresh story: Junjou Mistake!