Spider's Web is the name of a special type of opium as well as the name of its unique method of manufacture. Spider's Web opium was developed for wealthy industrialist Takeda Kanryū by a corrupt physician in his employ. Using a special method devised by this doctor, Spider's Web can be produced in half the time and with half the cost as normal opium but has twice the potency, instantly quadrupling profits from its sale even at reduced prices. The doctor, hoping to make a great deal of money with his invention, only revealed its production methods to his assistant, Takani Megumi while withholding its secrets from Takeda. Unfortunately, Takeda's zealous attempts to obtain the method resulted in the doctor's death, leaving Megumi the secret's sole inheritor.
However, while Megumi was forced to remain under Takeda's control and produce Spider's Web for him to distribute, she refused to divulge its complex manufacture process so as to lessen the number of people exposed to it as much as possible. While this made her indispensable to Takeda, it also virtually ensured that she would never again be free from his influence.
Through Takeda's channels, Spider's Web was distributed at low prices throughout Tokyo, resulting in many addicts and overdose-related deaths -- like that of Yoita -- until Megumi finally fled Takeda's compound and sought the help of Himura Kenshin. After Kenshin and his friends confronted Takeda and had him arrested, the manufacture of Spider's Web ceased forever.
- The concept of Spider's Web is based on the real-life drug crack cocaine, which is both cheaper to produce and more potent than normal cocaine and has led to serious problems in urban areas since its development in the 1980s.