I wonder if Hebikawa is gonna get relegated to just a side character after this arc. This might be the end of her time as a “rival”, even if it just barely started.
Hebikawa is as much a main character as Kusunoki. Arguably almost more than Keisuke, given the focus of this series
is Kusunoki and the changes to her character from childhood to now.
She and Hebikawa are counterparts and diametrically opposed in their worldview and way of interacting with the world. Hebikawa is "Dark", Kusunoki is "Light". It's why Hebikawa is so obsessed with the idea of revealing the dark she's convinced exists within Kusunoki; they were similar as kids, had similar formative experiences involving threatment at the hands of classmates and others close to them, and went in opposite directions from that watershed moment.
Hebikawa is as integral to Kusunoki's plot as Kusunoki is for Hebikawa, because both are needed to expose "the truth" about the other.
Hebikawa being "relegated to just a side character" would be the author completely ruining this series and misunderstanding the point of their own writing.