Ahem, I only just realized that Sumireko is wearing a Quimbaya airplane (just google it, or "Quimbaya artifact") pendant. Those pre-Columbian artifacts were a famous "evidence" for ancient astronauts, even though they were simply stylized fish. (For example, see
Ancient Aliens Debunked)
It's ironic that according to her vs. mode dialogue, Sumireko does not believe we have any chance of meeting intelligent aliens, meaning the pendant is only part of her spooky occultist getup, not something she believes.
It's doubly ironic that non-alien ancient astronauts do exist in the Touhou universe, in the form of the Lunarians, who might be manipulating Sumireko, and whose powers Sumireko have tapped into with her last word.