I Become Stronger by Killing People in the City

A small character accidentally obtained the system of killing people and becoming stronger. As long as you kill someone, you can absorb the spirit of the slain person to strengthen yourself, and you can even obtain the memory of the deceased. Faced with a shortcut to becoming stronger, will the protagonist become murderous and eventually sink, or will he gain the last light in his heart through killing? PS: The protagonist will eventually travel to other worlds This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.