"Kubisuji Line" (首すじライン?) is Rythem's fourteenth (fifteenth overall) single. It was released on February 20, 2008 under the Sony Music Entertainment Japan label. The title track was used as the theme song for Nikkatsu Co. Ltd.'s film entitled Naoko. Aishikata was used as the campaign song for Nippon Travel Agency Co., Ltd.'s Akai Fuusen Sotsugyou Ryoukou. While Nekoze (acoustic version) was used as the theme song for Nippon TV's Shiawase no Shokutaku.
This single contains a limited and regular edition and these two editions have different track listing. The item's stock number is AICL-1916.