Eirin Yagokoro (八意　永琳 Yagokoro Eirin) is a Lunarian who was involved with the founding of Lunar Capital on the Moon alongside Lord Tsukuyomi, before fleeing from the Lunarians to Earth.[5] She's an archer and medical genius who created the Hourai Elixir with the help of Kaguya Houraisan's power to control eternity which lead to her living in Eientei after choosing to stay with and devote herself to Kaguya on Earth rather than take her back to the Moon.[6] She first appeared as one of the alternate Stage 6 bosses and main antagonists in Imperishable Night and created a medicine, the Ultramarine Orb Elixir, that removes the impurities in Legacy of Lunatic Kingdom. She is also the instigator behind the events of Fossilized Wonders. Eirin is an enigmatic person surrounded by many mysteries and her answers regarding the mysteries about her are incoherent replies. She is generally a fairly pleasant person and is devoted to serving her ally, Kaguya, but she does not suffer fools gladly, and because of her incredibly high intelligence, she can come across as conceited, impatient and condescending at times to those not sharp enough to follow her explanations immediately. However, she also seems to lack general common sense, most likely due to her not living with humans. Abilities Making any drug She can make all sorts of drug/medicines, from medicine for the ordinary cold to drugs that can manipulate dreams. As one would expect, she is not able to make medicines that would require a physically impossible process in order to produce, nor can she make the medicine if she does not have the ingredients. Although she did make the Hourai Elixir, she made it using Kaguya's ability. Natural Genius Eirin is said to be highly intelligent and considers other people to be less smart than her. Furthermore, the Yagokoro family is said to be a line of medicinal geniuses and even among them, Eirin is exceptionally intelligent. Due to this, Eirin is rarely understood by others. Immortality It is not specified in her profile, but Eirin reveals to Yuyuko in the Netherworld Team's Good Ending of Imperishable Night that she has drunk[7] the medicine made with Kaguya's ability, in order to not die. Yuyuko's response and further narration cement that this is referring to Eirin having become immortal, from the Hourai Elixir. Other abilities Aside from her medical knowledge, Eirin seems to be very skilled in various forms of magic. For instance, in Imperishable Night, she sealed the whole Earth preventing anything or anyone from reaching or leaving it. Additionally, she replaced the real Moon with a fake one that was able to mislead the heroines with an illusion. According to herself, doing this was "hardly" her most powerful spell, meaning that she is probably able to use other types of sorcery that are far stronger than this[8]. Occupation After the events of Imperishable Night, Eirin has begun using her knowledge of medicine to act as Gensokyo's premier pharmacist, selling medicines at Eientei ranging from sleep aids to various cures. You can visit her like you visit a normal doctor, and she can even prescribe medicine for obscure illnesses. Her medicines are well known to work with no side effects, though youkai medicine and human medicine must never be mixed together. It's reasonable to believe her medicines come from the Moon or are developed with Lunar technology. The medicine is not only effective, but fairly priced. Fortunately, Eirin is not fussy about payment; she will most likely wait until you pay her. Still, it is believed that Eirin may have another reason for starting this business other than profit. Possessions Bow and Arrow Eirin wields a bow and arrow. Presumably, she uses it for spellcards. Ironically, she has never been seen using arrow bullets in any of her spellcards. Spell Cards Spellcards Backstory A long time ago, Eirin was the Sage of the Moon; with her high intelligence and the aid of the former Princess of the Moon, Kaguya, she created the Hourai Elixir and gave it to her. As a result, Kaguya was exiled to Earth as a punishment for drinking the elixir. A few years later, Kaguya had been allowed to return to the moon and, along with other Lunarians, Eirin was sent to Earth as an emissary from the Moon. Eirin felt guilty because she herself wasn't punished even though she was the one who made the elixir. Her desire for redemption was so strong that she was ready to do anything for Kaguya, and so she killed all the other emissaries and decided to live on Earth with Kaguya as her own punishment. After living a few hundred years hidden in the Bamboo Forest of Gensokyo, her whereabouts were discovered by the Moon, and led to the Eternal Night Incident, but at the time the incident was resolved, she came to know that even if she did not try to hide the Moon, the Lunar Emissaries wouldn't be able to come for Reisen. She has been living as a resident of Gensokyo ever since. Character Design Eirin illustrated in Perfect Memento in Strict Sense Origin Eirin is likely based on Ame no Yagokoro Omoikane no Mikoto (天八意思兼命), the god who thought of the plan to lure Amaterasu out of hiding. This can be seen by her spell card, and by the correlation between Eirin's sharp intellect and Omoikane's. (Takami-Musubi is also very strongly associated with intellectual facilities.) The interrelationships of various lunar figures presents a more interesting situation. Eirin is distantly related to the Watatsuki sisters, both based on mythology. In the third chapter of Cage in Lunatic Runagate, Watatsuki no Toyohime mentions that Eirin's participation was critical to the founding of the lunar capital, and that she was older even than Tsukuyomi. Omoikane is the son of Takami-Musubi, one of the great gods that summoned Izanagi and Izanami into existence, but it's unclear whether Omoikane was born before the creation of the Japanese islands, which also saw the births of Amaterasu, Tsukuyomi, and Susanoo. Name Her full name is Eirin Yagokoro (八意　永琳). The characters for Yagokoro (八意) literally means "eight minds" and Eirin (永琳), "eternal jewel". The number 8 in Japanese culture signifies the sacred and the infinite, and is often used indefinitely to mean "many" or "countless" (as in the Eight Million Gods). Gokoro is an ancient reading for 意, which could indicate something about heart or mind. So her whole name could mean "Intelligence of eternally clear brightness over infinitely extended area", referring her to be the "Mind of God". It is revealed in Silent Sinner in Blue that "Eirin" is merely her earth name, her true Lunarian first name being unpronounceable to the impure earthling tongue. Regardless of "Yagokoro" in both cases, she is strongly implied to be Omoikane. Design Eirin has dark grey eyes, long silver hair, has a large braid on her back and carries a strange pair of bow and arrow. Her clothing is red and blue and is covered with constellation patterns, though in her original appearance it’s closer to being red and black. She also wears something similar to a nurse's cap. Eirin's clothing has trigrams (broken and solid Yin/Yang lines) lining the bottom hem. They appear to be the complete set of trigrams used in Feng Shui, and match the set of trigrams on the Hakkero. Appearances Games Spin-offs Literature Imperishable Night Eirin's sprite in IN During the events of Imperishable Night, Eirin attempted to seal the passage between the Earth and Moon, which opens every full moon, by casting a spell that would seal the Earth inside a chamber (similar to a Chinese folktale about a paradise found inside a pot). She only meant to do this to protect both Kaguya and Reisen so that the emissaries coming from the Moon wouldn't be able to reach them, but this did not go unnoticed by the various Youkai in Gensokyo who enjoy the moonlight. Legacy of Lunatic Kingdom Eirin is involved in the backstory of Legacy of Lunatic Kingdom. The Moon habitants decided to make an invasion to Gensokyo with the intent of purifying it. Moon rabbits and mechanical spiders are razing the place and leaving a lifeless Earth. Gensokyo's humans can't fight by themselves, because a simple error means death, and it also looks like the youkai for some reason can't interfere with the purification, but Eirin planned ahead for such event and made a medicine that allows the user to see the close future. She sends Reisen to give the medicine to Reimu Hakurei, Marisa Kirisame, and Sanae Kochiya and resolve the incident. This medicine is the tool that allows the Pointdevice gameplay mode, in which the player cannot get hit once. Eirin in HM Shoot the Bullet Main article: Shoot the Bullet: Level 9 Spell Cards In Shoot the Bullet, Aya Shameimaru encountered Eirin on stage 9 and took photos of her danmaku. Hopeless Masquerade Eirin made a background cameo appearance in Hopeless Masquerade on the Human Village stage. She is seen sitting on a bench with Tewi Inaba, Kaguya Houraisan and Reisen Udongein Inaba drinking something. Bohemian Archive in Japanese Red Main article: Bohemian Archive in Japanese Red Article and Interview: Eirin Eirin has created a new medicine called the Kochoumugan (Butterfly Dream Pill), which guarantees that one will have a pleasant dream. She says that since the youkai of Gensokyo rarely suffer from physical ailments, she began developing medicine for spiritual ailments instead. This particular medicine is ancient, but humans who took it in the past often found their dreams too enjoyable and never returned from the dream world, so Eirin has weakened its potency and made it safe to use. She also has a variety which causes nightmares instead of pleasant dreams. In the interview, Eirin remarks that only a few people have come to buy the pill, even though it was a featured article in Aya's newspaper. Aya admits she doesn't have many readers. She is curious who is buying the medicine; Eirin is initially reluctant to say, but then reveals that it was Alice Margatroid. Aya mentions that she tried the pill herself, but found the dream uninteresting. Eirin suggests that she try Kochoumugan Nightmare Type (a scene in Shoot the Bullet). Whispered Oracle of Hakurei Shrine Main article: Whispered Oracle of Hakurei Shrine: Eirin Yagokoro Reimu Hakurei writes a fortune slip about Erin as a way of cleaning up in the aftermath of an incident. Relationships Kaguya Houraisan Kaguya is Eirin's master and friend. She made the Hourai Elixir for Kaguya which resulted in her banishment. Feeling regretful, when she was sent to Earth to bring her back on the Moon, she killed the other emissaries and helped Kaguya with hiding herself. Now she serves Kaguya faithfully at Eientei. Reisen Udongein Inaba Eirin's servant. Eirin has employed Reisen's telepathic abilities to gain intelligence on the Lunar capital. She also sends Reisen to the Human Village to sell her medicine. Tewi Inaba Tewi made a deal with Eirin to defend Eientei in exchange for Eirin imparting her knowledge to the rabbits. Thus Eirin is an ally, employer and teacher to Tewi and Tewi appropriately addresses her as Master. Eirin realizes Tewi's importance to Eientei due to her control over the rabbits and despite Tewi's pranks, knows that Tewi is there whenever they really need her, should the circumstance arise. Watatsuki no Toyohime & Watatsuki no Yorihime Eirin was a teacher to both Toyohime and Yorihime. They both respect Eirin with much admiration even after Eirin became a fugitive. They both are also distantly related to Eirin through marriage to their unnamed husbands (one of the Watatsuki sisters was the wife of Eirin's grandnephew, while the other one was married to their son[10]), Lord Tsukuyomi Not much was known how close they are, however they both founded the lunar capital together, so they could have been in good terms. It's unknown if their relationship remains the same after Eirin's desertion. Medicine Melancholy After learning of Medicine from Reisen, Eirin goes to the Hill of the Nameless to meet her. Eirin takes an interest of her thanks to her poison abilities. Minor Relationships Alice Margatroid Alice regularly purchases the Butterfly Dream Pill from Eirin. Sakuya Izayoi According to Eirin's profile, Eirin was very surprised to see Sakuya during the events of Imperishable Night. Though what relationship they have are unknown since only Eirin knows the reason why. Misumaru Tamatsukuri Eirin asked Misumaru to create the incident stones before the events of Fossilized Wonders. Ariya Iwanaga Eirin asked Ariya to freeze Gensokyo into an internal loop in order to stop the impurity coming from the outside, while guaranteeing her that the protagonists would come and defeat her, before the events of Fossilized Wonders.[11] Eirin disguised’s cloths Reisen has red eyes, long light-purple hair and long rumpled rabbit ears - like all members of the Lunar Defense Corps[18] her ears stand up straight and are decorated with two accoutrement-like buttons. Her outfit consists of a long-sleeved black business suit over a white shirt and a red tie, along with a beige skirt, white socks and red shoes. Her left lapel is decorated with a crescent moon-shaped insignia, and a pocket square in her left shirt pocket.

Kaguya thinks Eirin looks like Red Bull : r/touhouEirin is an intelligent, dedicated, and often exasperating individual whose personality is a mix of brilliance, impatience, and a lack of common sense. She is a genius, particularly in medicine, and can come across as condescending to those who cannot keep up with her explanations. Despite her high intellect, she has a notable deficiency in practical, everyday common sense, possibly due to her isolated upbringing on the moon. She is fiercely loyal to her friend Kaguya and can be a fair-minded, pleasant person, but she does not suffer fools gladly. Intelligent and knowledgeable: Eirin possesses an incredibly high intellect and is a medical genius, able to create complex elixirs and drugs. She is often seen as the "brains" of any group she's in and has an unparalleled analytical capacity. Condescending and impatient: Her genius can make her seem conceited, impatient, and condescending, especially when explaining complex topics to those who are not as sharp as her. Lacking common sense: Despite her brilliance, she often lacks basic common sense, likely due to her long time spent on the moon and not living with humans. Loyal and dedicated: She is fiercely devoted to her friend Kaguya and will do anything to protect her, having chosen exile on Earth rather than return to the Moon to take Kaguya back. Enigmatic: She is surrounded by mystery, and her answers to questions about her past are often incoherent.