>>1850988http://exhentai.org/g/857269/3ade7f9929/Basically, Maki needs to pee/poop, enters a stall which Nico is already using and accidentally sits on her. Then for some reason they get locked in, and now Maki needs to poop. She tells Nico not to look [spoiler:lit](girls telling people not to look at them while they're peeing/pooping/about to go is my fetish, by the way)[/spoiler:lit] as she sits and takes a shit, which is depicted as a SIF combo sequence (which by the way spells out 25252 which in Japanese resembles Nico's catchphrase). Later on, it's Nico who needs to continue her pee, and after some hesitation she does go, only for Nozomi to discover the two.
