Toramaru

Toramaru is a large biker gang led by Rokujo Chikage that is primarily based in Saitama. They act as antagonists in volumes 04-06 of the light novel series but have since taken on a more passive stance in the story due to Rokujo and Kyohei's newfound friendship.

History
Not much is known about  Toramaru's history before the start of the series. All things considered, they appear to be one of the more charismatic biker gangs within their area. Although there are a few hotheads in their group, they generally don't start too much trouble beyond the usual noise complaint unless provoked.

Role in the Plot
Volume 04: Toramaru makes it's first appearance in Durarara in this volume. A few members, bored and looking to make a quick buck, find Yodogiri's 1 million yen bounty on Celty and decide to go for it against the orders of Rokujo. They split up and start combing the city for Celty and one group comes across Mairu and Kururi who are also looking for her. The twins passively insult them which, of course, causes them to attack. However, they are thwarted by the timely intervention of Kyohei and his crew. The Toramaru  members gives chase to Kyohei and the others across the city, occasionally attempting to attack the van with whatever they happened to be carrying at the time (crowbars, pipes, etc).

Meanwhile, the other half of the group  managed to track down celty and started chasing her across the city as well. The groups eventually reunite and attempt to drive Celty and Kyohei's group into a corner. Kinnosuke Kuzuhara as well as several members of the traffic police attempt to intervene but only manage to succeed to taking out a fraction of the group.

Toramaru eventually corners Celty and the others but, as they close in, Ruri Hijiribe appears behind them  and attacks. Egor also appears, bursting out of a sack that Celty had been carrying the entire chase, and joins the fray as well. Egor and Ruri eventually defeat the Toramaru members and force them to retreat. Bruised and humiliated, a few members attempt to beat up Shizuo to vent but only end up getting sent to the hospital.

Volume 05 - 06: At some point in between volumes, Several Toramaru members along with various friends and family members who weren't directly in their gang were attacked by remnants of the Blue Squares led by Aoba Kuronuma who were posing as members of the dollars. Many of them were injured and hospitalized and in retaliation Rokujo Chikage and several others went to Ikebukuro for some payback.

For the most part, the gang itself stayed on standby while Rokujo did most of the legwork, eventually singling out Kyohei as the Dollar's "Leader" and challenging him to a one on one match. While the two of them fought, a few rogue Dollar's members attempt to use one of Rokujo's girlfriends, Non along with a few of her friends (Rio Kamichika included), as a hostage to get him to back down. The tactic fails as Kyohei's friends, along with several dollars members who were against using hostages, intervene and save the girls. Rokujo calls in the rest of his gang and the fight escalates into a full on brawl between the kidnappers vs the Toramaru/Dollars alliance. The battle gets even more chaotic as Varona, Anri, and even Shizuo arrive for various reasons. Eventually, the Kidnappers are dealt with and Rokujo orders everyone back to Saitama.

Notable Members
Rokujo Chikage (leader, founder?)

Non and various other girlfriends of Rokujo (not members per se but still affiliated indirectly)