Alchemist
The hero unexpectedly inherits (as the only relative) a house and a good piece of land from his great-uncle. The truth is quite far from the city.
The hero did not remember him for a long time, absorbed in his affairs in the city. However, at a certain moment, a whole bunch of troubles fell on the Hero and he decided to wait it out and restore his nerves in a house in the village.
Upon arrival, as expected, he saw a rather heavily lopsided house. However, it is still quite residential. Suddenly finds a super modern bunker room there. And there he even finds a very thick and rare book. And he experiences the greatest shock when the book starts talking to him!
It turns out that his Great Uncle was a gnome alchemist and quite famous. But at some point, he created a potion of epiphany, drank it and took all his potions, but at the same time leaving the most valuable item - a book, dumped in an unknown direction.
Everything was amazing for the Hero, from the fact that gnomes exist and one of them is his relative, ending with a talking book.
The book tells him that there are many worlds and in the world familiar to the hero there are no those fantasy creatures. But in other worlds they live and live well. And they periodically visit this world. The world is located at a crossroads, albeit remote. Therefore, there are enough "visitors" here.
A prohibition on telling the supernatural is imposed on every magical creature. Due to the fact that in this world it is very difficult to conjure. And any magician capable of burning many thousands of armies in other places is no worse than a flamethrower in ours. Therefore, the magical inhabitants will not be able to defend their lives if suddenly ordinary people rise up against them. They tried once, but it all ended with the Inquisition and going underground.
Therefore, the magical ones were very disapproving of the disclosure of their secrets and by any means, even lethal ones, sought to preserve it.
And the book itself is a unique artifact created by the greatest alchemist for teaching future generations. Simultaneously being both a teaching aid and a teacher.
But it was so long ago that the name of the magician has already been erased from the memory of even long-lived creatures. And the book is still intact and has trained more than one hundred alchemists, both mediocrity and the greatest magicians. The main character's grandfather inherited from his mentor. And now, apparently, the book is inherited by the Hero.
First of all, the book teaches the Hero to make a potion of true vision, which will help him see the world as it is, without magical illusions for ordinary people. When the Hero creates it and drinks it, he discovers a lot of new things. For example, that his appearance is somewhat different from the one to which he is used to, and he really looks like a dwarf in places. Secondly, there are a lot of magical creatures, places, objects, etc. in the world. Not at every step, but at least if you walk slowly through the city, you will surely meet something magical once an hour.
Next, the Hero begins to learn alchemy and use it to achieve his goals. The book does not condemn or praise him for his moral decisions, only for the ability to search for ingredients and brew potions. And as a skillful teacher, knowledge gives metered, offering a new recipe only after the Hero learns to cook the previous one without mistakes.
And everything would be simple and easy, but after a while (1 third of the game) the hero finds out that the magician is hunting for the book and is going to get it at all costs, even at the cost of killing the previous owner ...
Thoughts: Potions will be categorized by difficulty. The hero will also have an alchemy skill, which will grow after a certain amount of potions. The difficulty for the hero will be that his cooking will not always be correct and will depend on his alchemy skill and the complexity of the potion. If you're lucky, the hero can brew a super potion at rank 1 of alchemy, but this chance will be VERY low. In the event that the Hero is unlucky, he will simply spend the ingredients.
The game itself should be heavily tied to finding ingredients. Perhaps the hero will also have the skill of searching, biology, zoology, mineralogy. Which will also help him find rare ingredients.
The potions themselves can be sold and received in return for magic money (for example, crystals). By the way, crystals can be exchanged for regular money and vice versa.