It was mentioned way back then that Yanda was Koiwai's kouhai/junior (hence why he was shown with more energy compared to him here). Although, the author haven't yet to make it clear on what terms their relationship actually is (it could be that he is his kouhai from childhood/school/work or whatever else).All this time I thought Yanda was just a weirdo who doesn't understand personal space, but is he actually related to Kowai?
NORWAY!!!!NORWAY!!!!!!!
wait, shit, wrong series