You're referring to the Magic Shop by Roninsong!
The story revolves around Kim Min-soo, a high school student who discovers a mysterious shop called "The Magic Shop" run by a strange old man. The shop sells magical items and abilities that can change a person's life, but at a cost. Min-soo becomes entangled in the shop's secrets and must navigate the consequences of his own desires. magic shop by roninsong full version top
The Magic Shop by Roninsong is a popular web novel and webtoon series that has gained a significant following worldwide. Here's a brief summary and a feature list for the top version: You're referring to the Magic Shop by Roninsong