■■■■■■■ ■■■■■ (later decoded to Maribel Hearn) is apparently a university student in Kyoto studying something known as relative psychology. It's said she can see boundaries. According to written records, she is surprisingly bold during investigations. ■■■■■ ■■■■■ (later decoded to Renko Usami) is apparently also a university student in Kyoto. Her area of study is known as super-unified physics. It's said she can tell the time by looking at the stars and deduce her location by looking at the moon. According to written records, she is surprisingly cautious during investigations.

Beyond the borders of Gensokyo lies the human world. Out there, the existence of youkai has long been forgotten by the humans that live there. Dividing Gensokyo and the human world is the Great Hakurei Barrier making travel between the two impossible... or so it should. The first president of the Secret Sealing Club, Sumireko Usami, ordinarily lives in the human world.

The Secret Sealing Club operates out of Higashifukami High School. Sumireko Usami formed the club due to personal circumstances and refers to herself as the club's first president. Sumireko decided it would be "an organization that reveals secrets" and intentionally gave it a misleading name.

The biological classification of modern (living) humans is as follows: Class: Mammalia, Order: Primate, Subfamily: Homininae, Genus: Homo, Species: Homo Sapien, Subspecies: Homo Sapiens Sapiens. The only thing that separates humans from non-humans is the information contained within their DNA.

"Renko, I wonder what this is." "It's a pitch black... photo?" Shades of indigo and orange in the sky were fading into dark swaths of purple, signaling that things were about to get started. Using the sunset to denote the end of the day is a concept of modern civilization, which has been set free from darkness. Whereas in a time long passed, the sun's setting brought forth the beginning of a new day. "I thought you could make the photo clearer by flapping it about and drying it." "That's not true, Mary. You need to warm it with your hands. But it doesn't seem like this is that type of photo." The Secret Sealing Club started investigating.