Asuka and Rei are catgirls

Asuka and Rei have human lifespans.

Asuka compares Rei to a doll.

Asuka is 19-years-old.

Rei is 20-years-old.

Rei is quiet, deadpan, and emotionless.

Asuka is grumpy, highly confident, but seems lonely.

Asuka is jealous of how perfect Rei is as a catgirl.

Asuka has a tendency to call people that annoy her "baka".

Asuka is usually grumpy 24/7, but if given milk, she'll be happy.

Asuka usually hisses when annoyed.

Rei seems to never get emotional.