Wild Adapter

. Wild Adapter was also adapted as a two episode OVA in 2014, which is set in the universe of the manga series.

Plot
"W·A," later identified as "Wild Adapter," is the name of a dangerous drug which transforms its users into an animalistic state; the users exhibit superhuman strength and a berserker mentality until the drug causes his or her organs to explode, effectively killing them. The corpses left behind by W·A are covered in fur and sport cat-like claws. The police are baffled by W•A even as they investigate the remains of W·A users, and the Yakuza wants it. Two powerful rival yakuza groups, the Izumokai and the Toujougumi are fighting to figure out and gain control of the source of W·A, a task made harder by the fact that no user of W·A have managed to stay alive after consuming the drug.

Amid this, 17-year-old Kubota, the first of two main protagonists, have somehow managed to stumble into the position of Head of the Izumokai youth group, despite not being a gang member before that. He is aided by the second-in-command, Komiya, in his yakuza jobs and it is through Komiya that he knows of the existence of W·A. Komiya is killed by the rival Toujougumi gang when investigating W·A, and Kubota quits the gang after Komiya's death, but not before taking out twelve high-ranking members of the Toujougumi gang, and disappears from the yakuza world.

Soon after, Kubota picks up a stranger with amnesia whom he names Tokitoh, and they start living together. Tokitoh has no idea of his identity, or why his right hand is a furry, clawed paw identical to the animalistic bodies of dead W·A users, yet he is still alive. Kubota and Tokitoh then set out on a mission to investigate W·A, hoping to discover Tokitoh's past at the same time. The manga details their quest to investigate every victim of W·A, and following up on any leads provided by Kou, a drugstore owner who is Kubota's current employer, or Kasai, Kubota's detective uncle. These tips however are usually red herrings or traps and lead nowhere.

In the process, Kubota and Tokitoh often get mixed up with the yakuza who are just as eager to seek W·A. Sanada, leader back of Izumokai gang and Kubota's former employer is fascinated by Kubota, and constantly keeps tabs on him. Sekiya, leader of Toujougumi just wants to get his hands on W·A. In their various clashes with the yakuza Kubota and Tokitoh rarely emerge unscathed, but they always manage to survive and make it out somehow, ready to follow the next lead.