Immortal Weakling 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

After retiring as a vigilante so he can live a peaceful life, Yagura gets trapped in a survival game that is far more than what it seems. Now he must come out of retirement and train a new group of heroes to protect his city — but will it really pay to be a hero?