The Mysterious System: Plot, Don't Make Trouble

He was defeated and spent the first half of his life in a killer organization, so he met Jun. However, the second half of his life was spent on revenge, also for Jun. However, as fate would have it, he was destined to be romantic, and he could succeed in flirting with girls, but why should he attack men? And who is the yandere behind him who is following him and stopping him from flirting with girls? (The protagonist is charming, but a bit scumbag.)