The first we see of Eri is when Naota returns to school after being hit by the Vespa Woman. She remarks that the bandage on his forehead looks bizarre, and wants to know what he's hiding. After Gaku explains that the Vespa Woman hits you and leaves a mark that shows you've been doing naughty things, she's even more curious as to what's under the bandage. That's all that's really seen of Eri until Episode 03, though she does make an appearance for a couple minutes in Episode 02 in which she sneers at Mamimi and has a near-encounter with Canti.