..you know, at that height, unless they are screaming, those high up or those below shouldnt be able to hear each other. Unless its super quiet...
but hey, minor details. Also, how does he know they are his classmates? Didnt he ran after MC? Did he suddenly ran back?
Also, last ch MC told the nurce to tell the inforcement to NOT come to the park..and now it was "lets wait for them to arrive.." 
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Embrace your sinful self, embrace the darkness
Embrace your sinful self, embrace the darkness