Desperate Beginning: I Slaughter Alien Civilizations

[Traveling to another world + training and upgrading flow + bounty hunter + counterattack in life] His parents died young, his sister was seriously ill in bed, and he was at the end of his rope. He took part in a life-threatening trial and discovered a different world from the Earth - the Origin World. He slayed demons in the city, collected bounties, and subverted the evil alien empire...