Tank Chair is a Manga/Manhwa/Manhua in english language, ACTION series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

Protecting his sister Shizuka from a bullet, the strongest assassin Nagi Taira falls into a coma. Against all odds, he regains his consciousness- but only when faced with killing intent! Thus begins a violent journey of recovery, battling the most dangerous foes.