[infectus]

Originally Posted by RandomAvatarFan

Answer:

Spoiler:

In Onikakushi, they were just there to make the viewer scared of Rena and Mion. Since you're seeing it through the eyes of Keiichi who is paranoid and afraid of them, the girls have cat eyes, because they are the object that is creating fear.

In Tatarigoroshi, they were there to make the viewer scared of Keiichi. At this point Keiichi had decided that he was going to kill somebody. That's pretty scary.

In short:
They're only there when the viewer is supposed to be afraid because cat eyes are cool and scary looking.

Spoiler:

But in that moment and in the full Tatarigaroshi we were still seeing things by keiichi's point of view. So it doesn't make sense for us to be scared of keiichi (our point of view).