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 Threebillion-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!