That is not the first time Harusame bully the Bokukawauso in fan-arts. Is there a private joke / seiyu connection or real-life thing that happened ?
The Harusame cosplayer hired for KC IRL events once hold onto a Bokukawauso plushie tightly (like in this pic) and it went viral. Since then whenever the cosplayer appears again she would carry around the same plushie and "bully" it.