Daze
Daze is the opening theme of Mekakucity Actors performed by MARiA from GARNiDELiA. The song was composed by Shizen no Teki-P (a.k.a. Jin) and a PV for the anime was illustrated and directed by Shidu. The full song was released on May 29, 2014 by Jin.
(Source: Kagerou Project Wikia)