Tank Chair (Manga) Vol 01 (Mature)

Living on Gui Cheng Island, called "the most dangerous city in the universe," is no easy task. Genetic doping is common for gangs to gain ultimate power. Shizuka, a young girl, takes on the most dangerous of assassin jobs, but she's not the one doing the killing. Rather, it's her brother, Nagi, a strong assassin who took a bullet to protect his sister, leaving him in a comatose state and having to use a wheelchair. However, Shizuka has figured out the key to waking her brother up: he must be faced with killing intent! Thus begins a violent journey of recovery, battling the most dangerous foes! Kodansha Comics
(W/A) Manabu Yashiro