Teikoku Kishin Volcamion

From Hifumi Shobo: Robou is a corporate drone with an extraordinary passion for giant humanoid robots. One day, he's deeply hurt when a colleague bluntly states, "There's no need for giant humanoid robots." Later that evening, he's approached by a being from another world who pleads with him to "fight using a giant robot." After some hesitation, Robou chooses to reincarnate in this new world. There, he finds himself inhabiting Volcamion. A mighty humanoid mecha revered by the Volcami Empire. Thus begins Robou's second life as a god within a giant robot.