Mah boi Shiraishi ain't going after them oppai because Kubo's plenty cute herself.
For real tho, I really like the dynamic of the two in this manga. It is somewhat a better Takagi-san where both sides receive damage. Kubo is a great teaser to her beloved but she also gets visibly bashful and flustered (not seen by Shiraishi but at least by the readers). There are also plenty of moments where she also feels sad and down (like in the White Day chapter) and also moments where she's not an omnipotent being (such as not being a great cook/baker). For me, there is balance in her moments of assertiveness and her moments of weakness which I find really great.