Reimu Hakurei is a mysterious shrine maiden with the ability to fly. When she heard of the moon soldiers' sudden arrival, she grabbed her purification rod and sprang into action. Marisa Kirisame is an ordinary magician. Her investigation into the Occult Ball had grown into something far larger. Sanae Kochiya lives on the Youkai Mountain and is a living god who causes miracles to occur. She could barely control her excitement when she heard a spider-shaped probe had appeared at the foot of the mountain. Reisen Udongein Inaba is a moon rabbit living on Earth. On the orders of her master, Eirin Yagokoro, she was making her way back to the moon in order to launch an attack.

The Lunar Capital is situated on the far side of the moon, which is isolated by a barrier, and is home to the Lunarians. Since its construction long ago, it has remained a pure land, absent of the impurities of life and death. Apparently, at the time when Lord Tsukuyomi was constructing the Capital, he relied on Eirin Yagokoro for assistance. The Watatsuki sisters are the current leaders of the moon emissaries and live in the Capital along with Sagume Kishin, one of the Lunar Sages, as well as Reisen and the other moon rabbits. Throughout its history, the Lunar Capital has supposedly been attacked several times by Junko.

The Moon is the Earth's only natural satellite. Long ago in Japan, it was written using the kanji for "large" and "shadow," as opposed to the sun, which was written with the kanji for "large" and "light." The Moon is approximately 238,900 mi (384,400 km) from Earth and has a diameter of 2,159 mi (3,474 km). It appears roughly the same size as the sun in the sky, which gives rise to total solar eclipses and annular solar eclipses. The full moon shines with a magnitude of -12.7, making it brighter than any star as seen from Earth, and it's also an exceptionally large satellite with a diameter roughly 1/4 that of the Earth's diameter and a mass 1/81 of the Earth's mass. Being so large, it is responsible for shifting the tides. This celestial body has had an enormous influence on human culture thus far.

Incidents and other disturbances of the like occur frequently in and around Gensokyo. Each time an incident occurs, it's the incident resolvers who spring into action, each with different reasons and motivations for doing so. Reimu Hakurei has a deep connection to all goings on in Gensokyo, and so almost always works to resolve its incidents. Marisa Kirisame has few hobbies or responsibilities, so tends to get involved in resolving incidents, albeit with a laidback attitude. Having a strong connection to religion, Sanae Kochiya mainly seeks to resolve incidents pertaining to gods. Finally, if an incident has any connection to the Lunar Capital, you can bet Reisen Udongein Inaba will be on the move under orders from her master.

"Whoa, what is this?! It's freezing!" "Who wouldn't be cold dressed like that though, Reimu?!" "No, she's right. It is cold. Look, the Lunar Capital is frozen!" "Is this another part of their advanced moon civilization?!" "Something's coming." "Another baku? No, this one's got a wing." "Hang on. Is that... Lady Sagume?!" "That's unusual. They're already surrendering. I feel like an alien invader!"