What was that NANA reference on their room number on chapter 15? Does this mean Shou-sensei is a fan of Nana? And if you're familiar with Nana, it isn't considered yuri but there's that very strong yuri vibe bet. Nana and Hachi (her name's Nana too), the two roommates.
And the way Keiko blushed when Ran wore her punk clothes! Thank you Sensei for teasing us more, for making our yuri hope gets higher with each new chapter
BTW, we have new secrets revealed: Keiko changes her fashion with every new partner, which might be due to her trying hard to fit and convince herself that she's straight (as to what Koneko pointed above). And Keiko's really taking care of Ran, huh. Just like what a lover does when her partner's in such a busy mode, typical yuri moves. But Keiko tries to conceal it by making those very straightforward notes, yeah we get it Keiko, you're definitely straight to damnation if you don't hurry up and confess to Ran.