The BS Situation of Tougetsu Umidori, Vol. 1 (manga)

A simple request quickly gets out of hand!It's a day just like any other for Tougetsu Umidori when out of the blue, her classmate Nara Yoshino makes a strange request: Help her catch the thief who's been stealing—her pencils…? But there's more to this eccentric little request than meets the eye, especially when a weirdo in a cat hoodie who calls herself "Bullshit—chan" shows up at Umidori's house. Who is this girl? Why does she know so much about Umidori? Does she have something to do with the pencil thief? What the heck does she mean when she says, "Let's kill lies!"? …And why is she holding a knife?!