Prisoner Riku is a Manga/Manhwa/Manhua in english language, Shounen 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

Born into a world beyond imagination, imprisoned for a crime he never commited. Young Riku’s life couldn’t sink any lower…or so he thought. Determined to survive no matter the circumstances, Riku now faces the impossible task of outliving a prison sentence in Earth’s worst penitentiary.