Kazan Seirenzoku Bidou (a Touhou LW original) refers to a type of volcanic micro tremor, distinguished by its long-lasting vibrations. This is an apt temperament for the Queen of the Underworld from the world delirious with New Year's celebrations. She has retained the same temperament. (Strong against Sun Essence, Moon Essence, and Star Essence, but weak to Wood Phase.)

The ability of Satori Komeiji (S2) from the world delirious with New Year's celebrations (a Touhou LW original). Her ability doesn't seem all that different from the S2 Universe Satori's. That said, this world has far too many interworld travelers. It seems that across all worlds, there are similar cases of taking in visitors from other worlds and making them family. This Satori had finally realized that her family's circumstances are not as unusual as she once believed, and that understanding lifted a long-held sense of isolation. At the same time, she understood that every such case was still unique and felt a subtle sense of pride in that. Satori Komeiji had seen and heard many things. The members of Myouren Temple sheltering a young Byakuren Hijiri. The people of the Divine Spirit Mausoleum supporting a little Toyosatomimi no Miko. Little Seija, and Shinmyoumaru Sukuna grown to normal height by the Miracle Mallet's power. Mini Okina, accompanied by her two servants acting as her guardians. Some of them have different hair or eye colors compared to their original counterparts. Some fight with entirely different bullets. Some can be recognized at a glance as being from another world, while others appear no different. But every one of them seems to be connected to their adopted family by a deep bond. They would deny it if asked, but a mind reader always knows the truth. Every Satori has a sister. That's just how it is. And this Satori, too, has a younger sister: the original Koishi Komeiji from this world. One day, she disappeared. Satori feels she vanished without an explanation. Maybe there was a reason, but Satori simply failed to hear it, because she couldn't read Koishi's mind. But she knows better. That is merely an excuse. Ordinary sisters can't read each other's minds, but the bond between them still exists. It was not that she failed to read her sister's mind. She did not try to understand her. She feels that was probably just the kind of person she must have been in the past. Because youkai live far longer lives than humans, they are believed to retain their memories for longer as well. Otherwise, it would be terribly impractical. This does not mean that youkai have a sharper memory than humans. They may appear careless or slow to humans, but that is because their lives unfold at a much slower, less intense pace. When time stretches on endlessly, there is no need to rush through it. Perhaps the youkai are like whales, with slower breathing, slower heartbeats, and a more relaxed perception of time, which makes humans appear endlessly restless. That difference is evident in battles of bullets. The attacks used by youkai bosses are elegant and more spaced out, repeating the same pattern over and over. Humans, on the other hand, move frantically as they fight, unleashing dense, sharply targeted shots. Humans constantly make new memories and forget them just as easily. Youkai take a far more leisurely approach, both to remembering and to forgetting. That is why eccentric researchers, such as magicians, stand out as exceptions among them. So what makes for an ideal medium to preserve information over long periods of time? Parchment? Bamboo slips? Paper? Magnetic disks? Optical disks? Semiconductor memory? The best option known is stone. Images and letters etched into stone can be passed down thousands of years into the future. But no medium lasts forever. Sooner or later, it deteriorates, and the information it holds fades away. To remember something forever is nearly impossible, aside from rare exceptions, such as the Child of Miare. However, even if they don't last forever, maybe youkai, with their long lifespans, can serve as living repositories of memory. The strata of the Earth hold the memories of the world. The deeper the layer, the older the memories engraved within it. Fossils are the most familiar example, but all things carry memory, which is why carbon dating works. But carbon dating itself is nothing more than a theory devised by humans. Its foundations are based solely on human reasoning. Youkai have their own ways of interpreting history and their own methods for determining truth. And Satori Komeiji has her own approach as well. It is no different from reading minds. The mind, the structure of the brain, and even the mythological structure of the cosmos and the Earth are all layered like strata. The Underworld lies buried within the crust, with an underground sun floating at its center and structures built beneath it. Beyond it lies only soil, with historical remains buried by the passage of time. There is no surface, no sky, no space―only soil. Other stars and other worlds are separate spherical spaces, perhaps reachable by digging far enough. The Queen of the Underworld's philosophy was sufficient to become her emotional foundation as a memory-excavating interworld traveler. Her sister, Koishi (S5), had also set off on a similar journey. "What's wrong, Satori?" The Koishi (F1) calling out to her wasn't her original sister. But even with different hair and eye colors, she looked the same. And although her personality was different, her little quirks and preferences had not changed. So then, how does one decide which one's the real one? Having a standard to determine that would mean she would have to choose, and she wasn't sure she could do that. But from her original sister's point of view, being mistaken for someone else would be unbearable. Which means no matter what Satori does, she would be trampling on her sister's existence. And that's something she couldn't do as an older sister. Koishi (S5), whom she once lived with, and Koishi (F1), whom she lived with ever since Koishi (S5) disappeared, were both her sisters. That is why she wants Koishi (F1) to know that she's welcome to stay for as long as she wants. Koishi (F1) sat before her, spreading photographs out across the carpet, carefully arranging them in an album. If only Satori could read her mind. Or rather, if only she had the courage to speak to her.