"Chikai" (誓い, "Vow") is Eiko Shimamiya's fourth single produced by I've Sound and Geneon Entertainment label.

It is set to be released on April 8, 2009, a year after releasing her third single "Wheel of Fortune".

The title track is used as the opening theme for Higurashi no Naku Koro ni Chikai (ひぐらしのなく頃に誓), the live-action film sequel for the first Higurashi no Naku Koro ni live-action film.

The single's catalog number is FCCJ-0003 for the regular CD-only edition since it won't be having a limited CD+DVD edition.

Overall, this will be Shimamiya's fourth tie-in with the Higurashi no Naku Koro ni series.