Nakura is a student that used to attend middle school with Izaya and Shinra and was one of the first members of the biology club that was founded by the two of them. In recent years, he has been an unwilling accomplice in many of Izaya's endeavors.
During middleschool, after Izaya and Shinra formed a new Biology club, Nakura was one of the first members to join (mostly because all the biology club did was water plants). All the clubs were supposed to make some kind of presentation for the school festival which would take place after summer break. Shinra decided to place the entire project on Izaya's shoulders. Instead of working on the project, Izaya and Nakura decided to create a gambling ring of sorts. Since it was baseball season, the students would place bets on which team would win the next game. After several bad bets, Nakura eventually lost all of his and even most of his parents, money. Desperate and irrational, Nakura stormed into the bioloby clubroom with a knife, threatening Izaya to give him all the money he lost. When Izaya casually refused, Nakura rushed at him with a knife. At the last second, Shinra, who had been arguing with Izaya just before Nakura entered the room, jumped in the way of the knife and got stabbed as a result. In a panic, Nakura fled the clubroom and wasn't seen for the rest of the day.
Izaya, seeing an opportunity, decided to take the blame for stabbing shinra so he could use it as blackmail against Nakura later. As a result, Nakura became an unofficial and unwilling business associate for Izaya for the next several years. In highschool, the two of them revived their old gambling ring from middleschool and named it "Amphisbaena." The group expanded but Izaya and Nakura abandoned it due to Izaya getting bored.
During College, the two of them also formed a "Experimental Legal Drug" club which was centered around studying the effects of Medicine (NOTE: The exact details surrounding this particular club are scarce and should be taken with the grain of salt). They formed the club with another student named Shijima who was very adept at experimenting with strange substances.
After that club was disbanded, Nakura had very little direct contact with Izaya save for letting the information broker use his name from time to time (this is where Izaya got the Nakura screen name from). He would also recieve strange packages every few weeks but he was told only to forward them to Izaya which Nakura does without question (he figured that the less he knew, the better). After the events of Volume 09, Izaya gives a call to Nakura to inform him of the recent turn of events.
He states that the group "Amphisbaena" which they formed in highschool had expanded without their knowledge and began encroaching on the Awakusu's territory thanks to one of their old "associates" who was nicknamed "Earthworm ." He also explains that their old friend, Shijima, had entered into drug dealing and was selling a new and hyper-addictive drug called "Heaven Slave." When Nakura asks what any of this had to do with him Izaya explains that both Shijima and Earthworm were using Nakura as a scapegoat. When "Amphisbaena" was first formed, Nakura and Izaya both used fake identities with Nakura's alias being "Lizard." Earthworm used the "Lizard' persona as the false Leader of Amphisbaena so that he would take the blame in case things went south.
When the drug club was formed, Nakura used the alias "Kumoi" which Shijima also used as a scapegoat when he formed the Heaven Slave group. If the Awakusu resorted to having a gang war with either Amphisbaena or Heaven Slave, then it would be Nakura who ultimately took the heat. Izaya explains that, since he effectively neutralized both groups, Nakura didn't need to worry at all about getting killed by the yakuza. After Izaya hangs up, Nakura yells and screams about how horrible his situation is and how he will most likely be indebted to Izaya for the rest of his life.