Blue Moon (a Touhou LW original) refers to a visually blue Moon or the third full moon of a season that has an extra fourth full moon. This peculiar temperament is fitting for this world's Kaguya since she follows a fateful cycle separate from the cycle of reincarnation through her ability to manipulate eternity and the instantaneous. Kaguya's temperament has been completely reconstructed. Her being has more or less fused with the Arcus Mass Driver, practically making her a manifestation of the full moon. She also acts like the Moon is the true ruler of the heavens. (Strong against Sun Essence and Metal Phase.) However, she has also accepted her fate to live on the Earth as an eternally impure person of Hourai. (Weak to Earth Phase.)

The ability of Kaguya Houraisan, who has almost reached the end (a Touhou LW original). Kaguya completely lost this ability due to a Lost Word. She is currently regaining it little by little, though not through restoring or replicating her old ability, but with a newly constructed original ability that formed a core to build upon. She has continued to travel across worlds to try and end the Lost Word Incident. Even if a Lost Word could erase a person of Hourai by erasing spacetime or the whole people of Hourai concept, Kaguya Houraisan alone has the necessary attributes to come out on top―namely her ever-mysterious ability. Perhaps the main reason why it is so mysterious is because there is no conceivable situation where she could use it to its full potential. However, this world's Kaguya has come face-to-face with the Lost Word Incident. The concepts of eternity and the instantaneous can be explained by the world of Planck units. These units of measurement are named after the illustrious physicist who first proposed them. They include Planck time, Planck length, Planck mass, Planck charge, and Planck temperature. Planck time is of particular note as it represents the shortest possible interval of observable time. The fact that time is not a continuous flow but a series of disconnected moments, like the pages of a flip book, breaks down all our intuitive conceptions of reality. It reveals that the vast world we see and feel around us is mostly empty due to all the holes perforating space and time. The instantaneous can be understood as the infinitesimally small intervals that make up reality, while eternity is the infinitesimally large voids between them. Offsetting a clock that ticks in time with the instantaneous, even just a little, will reveal a world of infinite nothingness. By escaping into this world, you can avoid any and all influences, preventing your history from being recorded. Things secreted away into this world can be retrieved from any time or place without suffering any wear or tear due to the passage of time. These are the effects and uses of this world's Kaguya's ability to manipulate eternity and the instantaneous. However, the abilities possessed by the other Kaguyas might be different. "God is in the details." ...No, in this day and age, perhaps it's more accurate to say that "Gods have been forced to live in the quantum fluctuations." With the pervasion of scientific knowledge, modern-day humans have relegated the old-fashioned concepts of gods to the fanciful imaginings of children. However, the "real" world they perceive is nothing but an "instant"―a single thread of the infinitely expanding tapestry that depicts the truth of every world combined. This truth far transcends the understanding of humans. Unfortunately, Kaguya did not possess the wisdom of Eirin. Nor the vindictive tenacity of Mokou. Again and again, no matter how many times history repeated, each time she came face to face with a Lost Word, she survived... and was left all alone. She hates it. That's why she refuses to give up and is determined to overcome the danger that currently lies in her path, regardless of how impure and sinful she becomes with each successive iteration. This should come as no surprise because Kaguya is the most selfish and stubborn princess in existence. Arcus Mass Driver: This manifestation of the Lunar Capital Expo is powered by Kaguya Houraisan's own thoughts and feelings. That's why it has taken the form of the bow that Eirin wields. The items recorded in it are not limited to the Moon treasures displayed at the Lunar Capital Expo but also include treasures that Kaguya used to own, such as the Jeweled Branch of Hourai, along with every item possessed by the Lunar Capital... In fact, it has recorded every aspect of the Lunar Capital's culture. This amounts to quite a wealth of information, but Kaguya's use of it is limited since tools only function in accordance with the magical power of the wielder. In the Lunar Capital, information is hidden from or doctored to suit one's station, so there should be a fair amount of data recorded in the Arcus Mass Drive that Kaguya can't access. However, a certain incarcerated goddess, who is also recorded in this device, helped Kaguya jailbreak it. Now that they're secretly working together, it is only a matter of time―proper time―until Kaguya reaches the place where the Lost Word Incident originated. Incidentally, the name Arcus Mass Driver doesn't just refer to a bow that shoots mass but also a robust arch-shaped structure and a leader of people―a driver of the masses.