Grain is a characteristic of the film and is not affected, in itself, by the developer. But the developer can affect the appearance of the grain, as noted above. Most films available today have at least reasonably fine grain. Some, like EFKE 25, have extremely fine grain. You usually will not be bothered by the grain with these films regardless of the developer. But the developer does affect the appearance of the grain. A developer like Rodinal and various "acutance" developers emphasizes apparent sharpness and may emphasize whatever grain there is. But with a very fine grain film, the sharpness is what you notice, not the grain. Fine grain developers etch away the edges of the grain and make it less apparent. But they may degrade sharpness just a bit as well. Developers like D-76 and Xtol are compromises that have fine grain characteristics but still produce good sharpness. Also, as noted above, there is no substitute for square inches when it comes to either fine grain or sharpness. A big negative is the easiest way to get both.