I don't think it was rushed. They clearly had "some" chemistry when Rin was introduced and after her second chapter. And after chapter 25, I think it's clear that Rin became an emotional anchor for Itsumi (which can be seen in the Arare chapter where it's mentioned that Itsumi didn't seem to...
Wow, has it really been a whole year? I remember reading this series back then and hoping for an update for months! I can’t even begin to express how thankful I am to you for picking up this series!!!!!!!!!