Does anybody else notice how Yuuto's pupils became x's after he went yandere? maybe it's an artistic choice of some sort. To signify his whole yandere arc.
You know, i've noticed a common theme in the story and it's even clearer now: no one knows how to love right.
Hiro kills people because she wants to know how they really feel, Kubaru doesn't understand love or even her own emotions and just toys with people in an attempt to feel something...