Looking back at the chapter with Hiiragi's past, it's clear Hiiragi learned some "survival instincts" from her abuse that keeps her cautious of others. Which on the bad side contributes to her social anxiety, but in situations like this rightly tells her this girl is dangerous and to not engage with whatever she's planning.She seems like she knows Tomikawa’s need for attention so she is dangling the idea thinking that they are friends to manipulate her.
Hiragi, presumably having experience with emotionally manipulative people knew she should keep her distance from her, which she took as a possible challenge,
Put a lego in her school slipper.KICK HER ASS HIIRAGI. SHUFFLE HER DECK. actually wait thinking about the themes of this story i feel like that violence might get really bad. trip her in the hallway?