Aurora is a female deer character owned by Osaki Eru.

Aurora is "bigger than a building", but has a regular sized head in absolute terms, so she has a tiny head (or small head).

Reference: https://www.pixiv.net/en/artworks/91124035

オーロラさんまとめ

ここ数ヶ月で描いてた落書きのまとめです。

この子はオーロラ（Aurora）と言います。建物よりデカいお姉さんです。
PFMOHにも出演してました。

Google Translated:

Summary of Aurora

A collection of doodles I've done in the last few months.

This child is called Aurora. She is an older sister who is bigger than a building.
She also appeared on PFMOH.