The regressed assassin

Liev was an arrogant, lavish, and useless son of one of the strongest awakened. One day, Liev got kidnapped but his family didn't save him, and greatly suffered for a year, he became an assassin to get his sweet revenge and make his family feel despair. As Liev was nearing getting his revenge he discovered that he was declared dead, Liev discovered that his family tried to avenge his death even after the downfall of their family. [Congratulations, you are chosen as a character!] Liev was given a chance to return in time but to protect his family and live the life he wants, he needs to get stronger. What would happen if an assassin has a cheat system?