One day when he was usually doing his shopping on a mail order site to search for a book to buy so he could read it while commuting. A book that had something like living a life in another world was put up for sale. The contents were very fascinating that the protagonist decided to buy it. However, it seems it was genuine article that he really woke up in another world the next day.
He began to feel anxious in this slow life but, he met a girl and found his new goal in life. His goal was to have multiple wives. It was the so called Harem. And so using his option of privilege to buy that came with his unknown job class, he began his adventure towards making a harem.