The Detective Is Already Dead, Vol. 3 (manga)

Due to my penchant for getting dragged into things, I, Kimihiko Kimizuka, an ordinaryhigh-school student, suddenly was asked to protect national idol Yui Saikawa's Threebillion-yen sapphire. When there's a detective, there's always a case, and so, another case begins for meand Siesta's heart's recipient, Nagisa Natsunagi.