Play the Nobel Prize
On the way home from school, Ling Xiaowen had been a hero and taught three bad kids a lesson for bullying a " dwarf." In order to repay Ling Xiaowen's kindness, the " dwarf " secretly followed Ling Xiaowen and gave him a " Universal God Ball."
It turned out that this " dwarf " was the grandson of the famous great inventor, Tesla, a hundred years ago. When Tesla passed away, aliens stole his brain cells, revived him with high-tech means to serve them, and strictly guarded him from leaving the country. However, he was still concerned about Earth, so he asked his grandson to secretly " descend " to give his treasure to a " good person " on Earth, hoping that he would understand the truth while " playing " and contribute to the advancement of human science and technology.
This " God Ball " was known as the Lightning Fireball by the people on Earth. It was a mysterious product of nature. Other than Tesla, no one could successfully make it.
From then on, Ling Xiaowen and the God Ball were inseparable. They " played " with the fun of their teenage years and the wonderful and unimaginable stories of their growth.
Very good fanfiction. The only thing I don't understand is, why is he so weak? I mean he is supposed to have a really strong body and is two years older than tanjiro, so then why are zenitsu, inosuke and tanjiro as strong as him. There is also the fact, that he still didn't use sun breathing or isn't he aware of how to use it? After all even if he didn't Tanjiro would've talked about it.