Its been some time but the novel starts in a scientifically advanced world and MC's parents make their children fight and winner gets to change body parts with loser (e.g eyes, arm). After that MC is put into deep sleep (for quite long) since the lab(?) was attacked. When he woke up somehow he ended up in a school and train his void and death power(?) there. That's all i remember...
It has been a really long time but I believe this is The Sovereign of Death on webnovel, its an original
I believe this is what you are looking for https://www.google.com/amp/s/m.webnovel.com/amp/book/11493136705406405