Eirin

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. 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.