His movements were precise and surgical. They were the product of talent and hours of practice. They were flawless, and they were deadly.
He is not some superhuman. He is just a highly skilled individual that knew how best to move in order to kill. Now that his body can't hold him back anymore, he can finally unleash his potential.
It is something he has always craved to do. If there were no virtual reality games, he would be an assassin just for the thrill of it, not for the money. That's why he chose to participate in God's Domain.
Sure, it would be nice to be able to heal any injury, regain his youthful body, and live forever, but those are not the main reasons why he is here. He is doing it just for the love of the game. So he would have done all of these even if there were no tangible rewards to have.