Sanseiu (a Touhou LW original) refers to acid rain, rain that became unusually acidic from absorbing acidic gasses in the atmosphere. This is an apt temperament for Momoyo, who is a giant, dragon-eating, venomous arthropod. Oomukade, who dwell deep within the Youkai Mountain in places like the Rainbow Dragon Cave, lack the three celestial Essences. Apparently, they are hated by everyone, just like the youkai of the Underworld. However, it seems Momoyo continues to dig holes because she enjoys it, which distances herself even further from all celestial phenomena. Momoyo is endowed with Metal Phase, because she likes mining, and Earth Phase, since she deals with ore. The cold and silent Metal Phase resists Earth Phase, because earth bears metal, but it is weak to Fire Phase, because fire refines metal. The encompassing and regenerative Earth Phase resists Fire Phase, because fire produces earth, but it is weak to Wood Phase, because wood parts earth. The combination of Metal Phase and Earth Phase cancels out any resistance or weakness to Fire Phase.

Momoyo Himemushi's ability as a oomukade. It is rumored, predominantly by the youkai at the base of the mountain, that Momoyo's ability lets her eat the allegedly strongest creatures―dragons. It is unknown whether she can actually eat a dragon or not, but she must be an incredibly powerful youkai if there are even rumors that she can. Oomukade and dragon-serpent gods have a vicious rivalry, as is shown with the oomukade of Senjougahara and Mount Mikami. Incidentally, both of these oomukade were slain with arrows. The oomukade of Mount Mikami, written about in the Otogi-zoushi (an ancient collection of folktales), is particularly famous for terrorizing a clan of giant serpents. One of these giant serpents happened to meet a human hero, so the serpent took the form of a dragon girl to beseech the hero for aid. The hero agreed to this request and successfully exterminated the oomukade, for which he was rewarded with many treasures by the Dragon Palace. This story is obviously a variant of the dragonslayer trope that has been used in myths and legends the world over. These stories are usually a type of coming-of-age adventure where a hero defeats a dragon, saves a high-class female character, and is rewarded with treasure. Perhaps the most famous dragon-slaying tale in Japan is the story where the god Susanoo slays Yamato no Orochi. There are also variants of this tale where the dragon is replaced with a giant or an oni, as is the case with the tale of Issun-Boushi and Momotarou... On that note, the hero who slew the oomukade of Mount Mikami received an inexhaustible bag of rice as one of his rewards from the Dragon Palace. This is the same as the Miracle Mallet, a magical item symbolizing wealth and riches. In the tale of the oomukade's extermination, the dragon is replaced with a centipede, and the high-class girl is replaced with a dragon. The tale was most likely created this way because of the Japanese people's perspective on dragons. In Japan, dragons are revered and worshipped. The origin of dragon worship in Japan is complicated, but it probably has its roots in the Dragon Palace legends based on Taoist philosophy and the dragon-serpent dharmapala that act as envoys for the Buddha. Dragon-serpents are being of light, so it makes sense that an oomukade was chosen as the representative of the bug youkai―beings of darkness that are hostile to these dragons. In the past, the bug youkai were so powerful that they reigned supreme for an age. This may be due to the fact that dragons became superior beings to youkai. It is probably hard for a person of this modern age to imagine a dragon losing to a bug. However, in the past, it was even believed that snakes defeated frogs but lost to slugs in a type of rock-paper-scissors situation, so it wasn't much of a stretch to think that dragon-serpents were weak to bugs. Bugs, in turn, were believed to be weak against frogs. However, dragon-serpents, centipedes, and slugs can also be grouped into a single category for beings that move by wriggling their body―worms. This is why the kanji characters for "snake," "centipede," and "slug all incorporate the radical that means "bug" or "worm." This connection may have also played a part in the formation of these legends. Momoyo, who lives in Gensokyo, is one of these legendary oomukade. Her relationship with Megumu is highly peculiar, considering that Momoyo is an oomukade greater youkai. Megumu has a connection with dragons since her name is written with the kanji for "dragon," so it would be interesting if Momoyo wanted to eat her... However, crow tengu, in part, originated from karura, which in turn derived from garuda. Garuda are inhuman beings that devour naga, and the dharmapala dragons originated from naga. Therefore it is possible that Megumu, as the boss of the crow tengu, is also a dragon-eater same as Momoyo.