Triage X Series by Shouji Sato

Mochizuki General Hospital boasts some of the most well-trained (and well-endowed) nurses in town. But though these ladies spend much of their day battling sickness, their after-hours are spent fighting a very different sort of disease...Under the leadership of the hospital chairman, a handful of staff members and local teenagers form a group of mercenary assassins, targeting the "cancers" of society and excising those individuals before their wickedness spreads.

Black Label continues its investigation into the distribution of Platinum Lily, a dangerous mind-altering drug that has hit the Tobioka black market. But its efforts so far have drawn the attention of a dangerous new enemy...

Mikoto--that is, "Miko Honma"--knew that going undercover at Misumi Private High School would carry some risks, but her support role quickly puts her on the front line of an all-out battle with Syringe! With the revelation that the school's shining star, Reika, is pulling the strings at Syringe, the pieces begin to fall into place--and the complete picture looks dire for Black Label!