Touhou Game Club

- She is not overly concerned with payment for the medicines.

- Her medicines are not only very effective, but carry a fair price. And even if you can't pay immediately, she will wait however long it takes for the payment.

- Even if you show up for an examination at a bad time, she will kindly examine you.

- And this is for both human and youkai.

- The fact that she has appeared all of a sudden and started treating people's illnesses, and yet doesn't seem to be motivated by money, gives an impression that there's something else to it.

- She seems like a kind human on a first impression, but since the reasons for her kindness are unknown, she sometimes makes people uneasy.

- She always follows this ideal pattern.

- But nothing for free.

- There are a lot of mysteries around Eientei, but she is the one most surrounded by them.

- Where did she gain her knowledge about medicine? Why can she make medicine for youkai as well? What was she doing before opening her pharmacy business? A lot about her is unknown.

- Her age is also unknown. Although she looks young at a first glance, her manner of speaking and behavior are characteristic of someone who has lived a long time, which only makes the question harder to approach.

- And especially strange is that, even though she possesses extensive knowledge, she is lacking of more general common sense.

- If you ask her about this, she'll answer with an incoherent response like that her skin looks so glossy because she made a rejuvenating medicine for that, and won't talk any more about it.

- Rumor has it that she is a human with a deep connection to the Lunar Capital.

- The fact that there are a lot of events and personages associated with the Moon at Eientei, and that rabbits are the ones to go around distributing the medicine seem to give support to this rumor.

- It wouldn't be strange if her advanced medicinal practice was the Moon's medicinal science itself.

- There's a possibility that, through some way, she has obtained the Lunar skills.

# The characters for Yagokoro literally mean "Eight minds", and Eirin "Eternal jewel". "Eight" (8) is the sacred number especially for ancient Japanese, and it could mean "sacred, numerous, infinite". For example, Yakumo (八雲, eight clouds), Yashima (八島, eight islands), Yata no Kagami, Yaoyorozu no Kami. And 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".

# 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.

# Although Eirin was the one who formulated the Hourai Elixir, it has never been explicitly stated whether she has consumed it herself or not. Her official profiles say nothing on the matter, and she never claims in-game that she is immortal, unlike Kaguya (who refers to herself as an eternal being) and Mokou (who flatly states she is immortal). Considering that she was punished far less severely than Kaguya was, it is possible that leniency was granted in consideration that she did not actually drink the elixir. While she is incredibly old, Lunarians do not die of natural causes. (She does acknowledge that she has prolonged her life through the use of drugs, but does not specifically mention the elixir; also, Yuyuko mentions her power of death will not work on Kaguya or Mokou, but offers no such caveat against Eirin).

# Eirin has a Spell Card named "Apollo 13" after the aborted third American moon mission launched in April 1970. The spell card's spell sign is "Curse of the Heavens", and seems to imply that it was Lunarian magic, not mechanical failure, that critically damaged the spacecraft and forced it to abandon its lunar landing so as to forestall the "invasion". It's also stated that the Lunarians know why the number 13 is cursed. Could Eirin have something to do with it?

# Eirin is often shown in fan works as using the many rabbits at Eientei, especially Reisen, as test subjects for various drugs and medicines. And according to Cage in Lunatic Runagate, she actually does sneakily give medicine to the rabbits.

# Eirin is often placed as doctor or nurse in fan works by obvious reasons.

# Eirin's Last Spell (Forbidden Arcanum "Hourai Elixir") is the only spell card that is shared by two characters (the other character being Kaguya Houraisan) in the whole Touhou series.

# She might be 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 Cage in Lunatic Runagate: Chapter 3, 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. Regardless of whether she is "meant to be" Omoikane, Eirin clearly draws on Omoikane in many ways.

# Eirin had recently developed a medicine called Kochoumugan (Butterfly Dream Pill), which guarantees the person who takes it will have a pleasant dream once they fall asleep. The medicine was featured in an article in the Bunbunmaru Newspaper, but still remains fairly unpopular (mostly due to the fact that the paper itself isn't too popular). There is one customer, Alice Margatroid, who has returned numerous times to purchase the medicine however, although the reasons why were never disclosed.

# In Inaba of the Moon and Inaba of the Earth Chapter 13, it is seen that Eirin wants to dissect and/or experiment on Suwako Moriya due to her similarities to a frog.

# In Tibetan Buddhism, the bow held in the right hand with an arrow in the left (as Eirin holds them) is a symbol of wisdom as a means of projecting method or skillful means.

# She is often grouped with Yukari Yakumo and Kanako Yasaka among the fandom, because their names contain the character å…«(which is sometimes read as 'ya'), which when misread, means "old hag".

# Eirin is sometimes parodied standing in a pose similar to G Gundam character Master Asia due to their similar hair styles and color. This could also be a reference due to the fact that Master Asia is refereed to as "Tohofuhai"(東方不敗) "The Undefeated of the East".

# The bow and the arrow are a possible reference to the huntress greek moon goddess Artemis (sister of Apollo; In Imperishable Night, ZUN made a joke about Apollo being the sun god, so he surely knows about Artemis). Artemis (or her bow) sometimes represents the crescent moon, symbol of full maturity in the cycle of life (it suits Eirin very well).
o Artemis is often assimilated to Selene (the personification of the moon), which is the root of Selenium, a non-metal antioxidant sometimes used as a medicine but toxic in large quantity to human beings. Antioxidants are known to improve life expectancy.
o Ursa Major, one of the constellations on Eirin's clothes, was originally Callisto, a servant of Artemis.

# Eirin may or may not be having any relation with Sakuya Izayoi.
In Imperishable Night, Eirin is very surprised to see Sakuya, and counting the fact that Sakuya is not affected with Full Moon (which said to make humans who look at it going insane).