Yui, who had wandered into the world of succubi, was training with Sacy, a succubus who had lost her body, to return to her own world. The training was, in essence, to enhance her powers as a succubus, which meant engaging in erotic activities. Yui, despite her embarrassment, managed to complete the training. However, one day, she heard that Ishe, the tool shop owner, was in trouble, and she went to the Gaia Mine to help. There, she found disheartened miners. "Alright! Yui-chan, time for training!" What should Yui do to restore their motivation? Succubi are the friends of working men... In order to return to the original world, my big brother Yui also trains as a succubus! Even the miners are amazed by Yui's unruly sexual skills.