The Ultimate Errand Boy is a Manga/Manhwa/Manhua in english language, Mangatoon 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

Ryunosuke Takagi, once known as the "Invincible Dragon" and the strongest brawler, is now a bedridden old man living with his grandson, Kent. Kent, who is bullied and forced to run errands for delinquents, struggles daily with his unfortunate circumstances. However, one day, an unexpected tragedy and miracle strike simultaneously, changing everything!