Yumemi is a goodhearted but extremely talkative gynoid attendant of an abandoned planetarium; she is designed to look like a young girl. Yumemi is slightly damaged and completely unaware of the changes that have occurred in the past 30 years, as none of the facilities and databases that she connects to exist anymore.

Therefore, she treats the protagonist like a regular guest by calling him "Mr. Customer" and speaks of the world as it was before the war. She fails to understand any information he tells her, other than things related to her job at the planetarium.

(Source: Wikipedia, edited)