Venturing into the wilderness, the skeptical Ryouta Murakami and the ambitious Kuroneko were on a quest to prove the existence of extraterrestrial life when a tragic accident occurred, reaping Kuroneko of her life and leaving Ryouta in a critically injured state. Ten years have passed since the disaster, and Ryouta is now living a normal life in high school. He vows to prove that aliens are real in honor of his late friend. A transfer student named Neko Kuroha unexpectedly arrives one day, bearing a striking resemblance to the late Kuroneko—even sharing a similar name. Most mysteriously, she seems to possess supernatural powers. As Ryouta takes more interest in Neko, he is drawn into a deadly world where dangerous scientists hunt magic-wielding witches that have escaped from their secret research laboratory. Neko is one of these escapees, but there are many others who are in similar situations, and it's up to Ryouta to protect them from their would-be captors.

The 7th Division's Private Hyakunosuke Ogata and former Shinsengumi Vice Commander Toshizou Hijikata find themselves on opposite sides of a gang war in Barato after hearing rumors of the Hidoro gang possessing an escaped prisoner's tattooed skin. With a lead to the hidden Ainu gold close at hand, the two gladly take up arms but a betrayal will force both sides to think twice before carelessly jumping the gun.

The race to obtain the lost Ainu gold is nearing its peak, as even more formidable ex-prisoners are set on keeping their tattooed skins intact. Saichi The Immortal Sugimoto and Asirpa can finally move forward together, but Asirpa's time with Kiroranke and Ogata Hyakunosuke has slightly altered her ambition and strengthened her determination. As their party leaves the Russian territory, they gain a peculiar follower. Meanwhile, Toshizou Hijikata's crew makes major moves to get invaluable skins, falling into the poisonous trap of a dangerous convict. Although each group possesses a strong advantage over the others, even First Lieutenant Tokushirou Tsurumi—the most powerful and ruthless contender—cannot advance without Asirpa's help. However, his ominous plans for when they will inevitably meet remain a mystery.

In early 1900s Hokkaido after the Russo-Japanese war, Saichi Sugimoto tirelessly pans for gold. Nicknamed Sugimoto the Immortal for his death-defying acts in battle, the ex-soldier seeks fortune in order to fulfill a promise made to his best friend before he was killed in action: to support his family, especially his widow who needs treatment overseas for her deteriorating eyesight. One day, a drunken companion tells Sugimoto the tale of a man who murdered a group of Ainu and stole a fortune in gold. Before his arrest by the police, he hid the gold somewhere in Hokkaido. The only clue to its location is the coded map he tattooed on the bodies of his cellmates in exchange for a share of the treasure, should they manage to escape and find it. Sugimoto does not think much of the tale until he discovers the drunken man's corpse bearing the same tattoos described in the story. But before he can collect his thoughts, a grizzly bear—the cause of the man's demise—approaches Sugimoto, intent on finishing her meal. He is saved by a young Ainu girl named Asirpa, whose father happened to be one of the murdered Ainu. With Asirpa's hunting skills and Sugimoto's survival instincts, the pair agree to join forces and find the hidden treasure—one to get back what was rightfully her people's, and the other to fulfill his friend's dying wish.