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

Due to my penchant for getting dragged into things, I, Kimihiko Kimizuka, an ordinary high-school student, suddenly was asked to protect national idol Yui Saikawa''s Three-billion-yen sapphire!? When there''s a detective, there''s always a case, and so, another case begins for me and Siesta’s heart’s recipient, Nagisa Natsunagi!