Chemist and Devil King

Sena Satou, a medical researcher, finds herself lost in a different world - and she is not the only one! After managing to start a new life as the medicine-man "Sena," she encounters a mysterious man. He is the demon lord Delmatitidis, a man of immense beauty and strong magics, but physically sickly and weak. He recognizes Sena's knowledge and experience in herbal medicine, and she becomes his personal apothecary. As they share time together, they form an unforgettable bond and soon the two are drawn to each other. A doting romance that will change the destiny of a genius but nerdy apothecary and the handsome demon lord!

(Source: Kadokawa, translated)