Kubo spits one of the strongest Romance/Flirt game currently seen amongst her age group in Romcom manga and Shiraishi barely sees her as a friend let alone a romance partner; but that isn't from lack of effort on her part, I wager she would dominate in any romcom where the MC isn't a black hole...
Kubo should teach the rest of these girls in the romance genre how it's done, she has mastered the craft of the flirt and any lesser MC would've folded by now.