p.s Bottom of the page.
Isn't that the guy's chest... And the part where that looks like that is between his neck and face? If that's what you're talking about.... Bottom left.
the semen trickling down his face while swallowing it.. and that was kokubo's shirt..
it's the seme's neck. the dark place is his goatee. and the line above is semen running down his chin..
http://www.mangago.me/read-manga/kibun_wa_joujou/mf/v01/c006/15/ What is this? It looks like a shirt getting sucked in...