Long ago, the king of Orvelia, Kyle, defeated the demon king Angmund and brought peace to the world. However, one hundred years later, demons have been sighted in the forests, threatening humanity once more. A scouting expedition is sent to verify the claim but only one member returns. Meanwhile, Riheet, the leader of a dark elf mercenary group, plots to take over Orvelia to exact revenge against the humans who forsook their race a century ago. The knight apprentice Kasel, accompanied by the priestess Frey, sets out to rescue Clause, an old friend who went missing in the tragic mission. However, along the way, Kasel discovers that he is the son of the revered King Kyle and the only one who can wield the Holy Sword Aea—the same sword that slew the demon king. To fulfill this destiny, the young knight must embark on a perilous quest, unseal the sword, and end the fear instilled by demons. As Kasel's journey to bring hope to humanity and Riheet's vow for vengeance intertwine, what fate could possibly await them?

What will happen when a desperate boy who grew up among evil people steps into the world of cultivating immortals? Immortals and demons can be separated by a thought, and life and death are not decided by heaven. Let's see how he goes against the current in this world where humans and demons coexist and evil spirits run rampant, and become a legend.

A man with a passion for vending machines awakens to realize that he has not only died, but he has also been reborn as one of his beloved machines! Although he is a modern appliance in a fantasy world, he requires money in order to keep functioning. He is stuck in one location until a young girl named Lammis stumbles upon him. Amazed by the drinks and food he sells, Lammis uses her "Blessing of Might" to lift him with ease and take him back to the village of Clearflow Lake. There, she officially dubs him Boxxo. Despite his inability to converse with the villagers, Boxxo becomes an essential part of the community. His goods provide nourishment, and, as he gains new abilities and products, he becomes a staple of daily life. Nobody is as loyal to Boxxo as his first and best customer, Lammis. The more time he spends with her, the more he tries to help her elevate her skills as a young hunter.

Humanity and demonkind have been on bad terms for millennia, resulting in the continent of Leunders being split in two. Although the situation has stabilized between the races, the fragile peace breaks when the new demon king launches a fierce all-out attack. With all of the non-demon nations falling to the violence in under a year, humanity's hope rests in a special squad, led by swordsman Kyle Leonard, that must assassinate the demon king in order to bring an end to the war. During the dangerous mission, Kyle ends up in a clash with the demon king that brings him to the brink of death. As Kyle realizes he has lost everything he wanted to protect, a mysterious gem transports him back in time before the conflict even started! Now with knowledge of future events and a strong desire to save his loved ones, Kyle sets out to become even stronger to prevent the extinction of humanity.