"Chikai" (誓い, "Oath") is the 25th single by Japanese band Do As Infinity, released on July 27, 2011.
The CD-only version contains the title track plus three live versions of songs featured on Eight.
These live versions were sung at the concert "Do As Infinity Live Tour 2011: Eight", recorded at Osaka Namba Hatch on May 15, 2011.
The main song, "Chikai", was announced to be used as theme song for a PlayStation Portable game named Sengoku Basara Chronicle Heroes, distributed by Capcom.
The CD+DVD version comes with a music video for "Chikai" and an original video of Sengoku Basara.