A typical save-the-world fantasy where Zion the male lead isekai by a door instead of a truck-kun. Along their journey, they experience a variety of environments and cultures, from the dark and dangerous dungeons, towers, pits, and portals of ancient civilization to the high-tech floating cities of humans. As time progresses, they also encounter a wide range of creatures and characters, from the powerful dragon to the mischievous imps. They encounter many obstacles that require the use of their newly found technology, ultimately leading them to the demon Lord's fortress and his generals. With the help of the dwarf kingdom, they are able to launch a full-scale assault on the demon's castle. As they get closer to their goal, Zion and Xiao form a strong bond. This leads to marriage and children. It all started with a door and an academy of magic.