World-class medical researcher Kanji Yakutani lost his little sister to a tumor years ago due to ineffective treatment. To honor her legacy, he has dedicated his research to developing new medications for such conditions. But as fate would have it, he overworks himself and passes away at the age of 31, only to be given a second chance at life in another world. When he wakes up, Kanji finds himself in the body of a 10-year-old boy named Falma de Médicis, the son of an esteemed family of medical practitioners in the Sain Fleuve Empire. Bearing the mark of a deity's divine blessing, Falma is capable of performing a unique divine art, allowing him to create and reduce any substance with the knowledge of its chemical properties. After reading through some pharmacology books, Falma realizes that this world is operating on similar medical practices as in ancient times. He also learns that medicine is an exclusive privilege to the nobility, depriving commoners of proper medical care. Using the knowledge from his past life and the divine abilities granted to him, Falma resolves to make medicine available to those who need it—irrespective of class.

Ron Kamonohashi, the best student in the history of the elite Detective Training Academy BLUE, has been living as a recluse since BLUE expelled him five years ago. Moreover, he is forbidden to work as a detective, having barely escaped execution after getting involved in a murder case while he was still attending the school. Ron's situation changes drastically when police detective Totomaru Isshiki, following the advice of a senior colleague, seeks him out for help with a criminal case that has remained unsolved for months. Ron reluctantly agrees to help Totomaru and uses his phenomenal intuition to discover the culprit in less than a day. However, it appears that Ron suffers from a mysterious condition that can cause those around him to lose their lives. To Ron's great surprise, Totomaru manages to save the life of someone whom Ron put in jeopardy. As the unlikely duo starts solving crimes one after another, BLUE sends operatives after its former student to find out if he has resumed investigative work. Fighting against murderers, rogue detectives, and the Metropolitan Police Department, Ron and Totomaru must join forces if they want to survive and see justice prevail.

The hero-king Inglis—who dedicated his entire life to building his country—is now approaching death. To award him for his honorable achievements, the goddess Alistia appears and grants him one wish. Having never been able to master the blade, Inglis asks to be reincarnated in order to do so. In a blink of an eye, Inglis finds himself born in the far future as a daughter of the Eucus noble family. Six years later, Inglis is discovered to be Runeless—incapable of utilizing the runes that enable the use of magic in this era. She is therefore ineligible to become a knight. However, this fits in well with Inglis' plan: she instead decides to become the squire for her cousin, Rafinha Bilford, allowing Inglis to focus on pushing her limits. For Inglis, the challenges this familiar yet different world has to offer are instead opportunities for her to hone her skills—and possibly become an extraordinary squire in the process.

Aileen Lauren Dautriche's life changes forever on the day her engagement with the crown prince Cedric Jeanne Elmir is nullified so he can be together with Lilia Rainworth. The event triggers Aileen's memories from her past life—she has been reincarnated in an otome game as the villainess, who is destined to die in the final act. To prevent her predetermined demise, Aileen has only one option: to court the game's last boss, Claude Jeanne Elmir—the proclaimed "Demon King" and Cedric's half-brother—and marry him. However, it is easier said than done, as Claude distrusts her intentions. Instead of giving up, Aileen adamantly tries to win his heart by helping Claude fulfill his wish: to build peace between humankind and demonic beasts. But time is running out, and it is up to Aileen to change the course of not only her tragic ending but Claude's as well.