Some urban legends are best left untested! Yuuto Suou gets more than he bargained for when he joins his childhood friend Mitsuki Shimoya in testing out an urban legend. When he uses his phone to take a picture of himself with the local shrine's divine mirror, he is whisked off into another world—one heavily steeped in the lore of the old Norse myths. Using his knowledge gained from school and from his solar-powered smartphone, he has the chance to bring the Wolf Clan, the same people who cared for him, to prominence, all while earning the adoration of a group of magic-wielding warrior maidens known as the Einherjar.

The game and anime follow Kon Hokaze, a boy who embarks on a journey from our world to an alternate world known as Mira, which is full a mysterious energy known as Alma. After saving Princess Ecarlate from attackers, he soon finds himself in the middle of a struggle around Alma.

In the kingdom of Earlshide, Merlin Walford was once regarded as a national hero, hailed for both his power and achievements. Preferring a quiet life however, he secludes himself deep in the rural woods, dedicating his time to raising an orphan that he saved. This orphan is Shin, a normal salaryman in modern-day Japan who was reincarnated into Merlin's world while still retaining his past memories. As the years pass, Shin displays unparalleled talent in both magic casting and martial arts, much to Merlin's constant amazement. On his 15th birthday however, it becomes apparent that Shin only developed his combat skills and nothing else, leaving him with blatant social awkwardness, a lack of common sense, and a middling sense of responsibility. As a result, Shin enrolls in the kingdom's Magic Academy to hone his skills and mature among other teenagers. However, living a normal life is impossible, as he is established as a local celebrity almost as soon as he arrives. Kenja no Mago follows Shin Walford's high school life in the capital as he makes new friends, learns about the world, and fights off the various forces of evil surrounding him and his city.

The day is as normal as it can be in high school as the students peacefully go about their everyday activities until an unprecedented catastrophe strikes the school, killing every person in its wake. Guided by what seems to be a miracle, a handful of students are fortunate enough to be reincarnated into another world as nobles, princes, and other kinds of people with prestigious backgrounds. One girl, however, is not so lucky. Being reborn as a spider of the weakest kind, she immediately experiences the hardships of her dire situation. Even so, she must press on to survive the numerous threats that endanger her life. Discovering that her new world has a system like that of an RPG, she tries her best to hunt prey and defeat monsters to level up and evolve. As she gradually grows stronger, she hopes one day her efforts will be rewarded, and that she will be granted a better life.