I've read "Mia and the Forbidden Medicine Report", "Apothecary Diaries" but I would prefer a regular book though instead of a light novel. Could be a thriller or a fantasy story, but I'd love it if the protagonist has to find the cure, maybe even in a race against time. Could be large scale (pandemic) or small scale (saving the little sister) but finding the cure should be a big part of the story.
Can take place in the modern world or in a fantasy world but I would prefer it if the illness itself was made up and not a real one currently existing if possible.
(You guys are the best at book suggestions, last time I asked I got such wonderful recommendations for my little relative who was overjoyed by the books I got him in the end, so thank you again for that!)
by Owlish_Howl