Right as he is about to earn a promotion, a salaryman meets an untimely demise. Taking pity, a mysterious being grants him a second life in the land of Galdardia as a teenager. Choosing the name Luciel for himself and a role as a healer, the young man sets off for the nearby town of Merratoni. There, he learns that healers are a coveted resource, yet they often take advantage of others for monetary gain. Vowing to be different from other healers, he joins the local branch of the Healers' Guild and begins unlocking his magical potential. After failing to save someone with his magic, Luciel is determined to get stronger. To improve his physical strength and hone his magic skills, he registers as an adventurer and takes rigorous training under Brod, the chief instructor of the Adventurers' Guild. Soon, Luciel gradually finds his way through Galdardia, gaining a reputation as a selfless healer who aids others regardless of expense.

The battle against the forces of evil is nearing its end as the Undead King Leonis Death Magnus remains the sole survivor of the Dark Lords. Standing no chance alone against his enemies, Leonis seals himself deep underground with the goal of reincarnating a thousand years later and rebuilding his demonic army. Within the span of a millennium, however, everything has changed. People no longer remember the great war that led to Leonis' defeat and instead face a new threat—the monstrous creatures known as Voids. Magical devices have replaced sorcery, and humans with special powers—manifested in the form of weapons called Holy Swords—train at the Excalibur Academy to fight the Voids. Reborn as a 10-year-old human boy, Leonis meets Riselia Ray Crystalia, a dutiful girl who stumbles upon the ruins of his hibernation chamber. Believing that Leonis has amnesia, Riselia offers him guidance and enrolls him at the Excalibur Academy. Leonis still intends to take over the world, but he must first familiarize himself with a reality completely different from all he knows.

Since ancient times, the citizens of Slantania have lived within a shroud of miasma, a force that brings forth monsters creating havoc around the world. When the kingdom's Order of Knights becomes incapable of containing the monsters, the Grand Magus summons a holy maiden—the legendary Saint—to obliterate the horrid creatures and restore peace. One evening, as Sei Takanashi returns home from a long day at work, a magical force pulls her into a foreign world. Upon her arrival to the kingdom of Slantania, she overhears that the Grand Magus inadvertently summoned two Saints—Sei and a brown-haired girl. Needing only one holy maiden, the prince declares the other girl as the Saint, leaving Sei to her own devices. Sei sets her sight on the Medicinal Flora Research Institute, an establishment known for its studies regarding herbs and potions. While indulging in her latest passion, Sei has a fateful encounter with the commander of the Third Order of Knights. But little does she know, her aptitude as a Saint will continue to exert its influence over her new life.

Not far from the town of Domina lives Shiloh, a boy who keeps hearing a voice in his dreams about a mission he must fulfill. But what mission could he be needed for remains unknown. That all changes when he meets two Jumi, a race that’s hunted for their unique gemstones, as a sudden outbreak of attacks against the Jumi occurs. His dream, his quest, becomes clear—help the Jumi and their gemstones! (Source: Crunchyroll)