Reiji Kirio, originally from Japan, escaped an unfulfilling life as a stressed and overworked office employee when transported to a fantasy world, an event he welcomed. In this new world, he discovered unique skills: "Medicine Appraisal" for analyzing botanical properties and "Medicine Making" for synthesizing advanced remedies far exceeding local capabilities. Initial disappointment at lacking combat skills turned to appreciation after he used these pharmaceutical talents to save the gravely injured werewolf girl Noela, who became his loyal assistant and companion.

He established Kirio Drugstore in an abandoned building within Kalta village, unknowingly sharing it with Mina, a ghost girl who proclaimed herself the shop's guardian deity. Using his skills, he revolutionized local life by creating practical modern products like dishwashing detergent, deodorizers, and pepper spray ("Capshin Fluid"), alongside enhanced magical potions such as the highly palatable "Super Energy Potion" that healed injuries and temporarily restored youth or vitality. His innovations attracted diverse clients: elves needing aim-correcting eye drops, dragons requiring cough suppressants, nobles seeking beauty treatments, and mercenaries using monster-repelling sprays. Despite the potency of his creations, he maintained modest pricing and rejected exclusive contracts with nobility, prioritizing community accessibility. His reputation grew to near-mythical status, earning him the reverent title "Medicine God" from some customers, though he consistently dismissed it, preferring recognition as a simple village pharmacist.

Socially, he remained oblivious to romantic interest from figures like the noblewoman Elaine, the ghost Mina, the elf Ririka, and the blacksmith Paula, partly due to limited prior relationship experience. He formed a surrogate family with Noela and Mina, showing protective instincts and patience despite Noela's functional addiction to his potions and Mina's covertly vulgar inner monologues. His pragmatic kindness extended to unconventional figures, including offering pity-based free services to a lovelorn Demon Lord who later became a part-time employee. Generally conflict-averse and dedicated to his "slow life" philosophy, he occasionally engaged in heroics, like personally sedating a rampaging dragon. His analytical approach consistently focused on solving problems through pharmaceutical innovation rather than combat, embodying a peaceful existence centered on community care and invention.