Teikoku Kishin Volcamion

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 into 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.

(Source: Hifumi Shobo, translated)