I'm not SURE, but for all the people asking what that pose could be in reference to I think it may be a reference to the pre-serialization doujins that this manga is lightly based on. They lean MUCH heavier into the bullying aspect of Nagatoro's relationship so they feel very different to this series and aren't really worth reading unless it's your kink.
They're here on Mangadex, though, with the title "Nagatoro-san Doujins". In the third chapter (Nagatoro-san's Sandbag) , Nagatoro kicks her senpai until he cries and the pose she takes when kicking is very similar to the one in this chapter. I think this chapter may be referencing it's origins here? Maybe planning to reveal some character lore soon? Dunno, but I thought that this was interesting!