Koroshi Ai (Love of kill)
I think this is much like Denki Daisy, except the mc is a killer and the love interest a bounty hunter. He also has a reason to protect her, but she doesn't know the full story. Its really kinda funny too. Struggling to find anything thats remotely like that though. Also, they are still translating the last volume (6), and only releasing 2 chapters a month. Thats so sloww! but reliable. Its at chapter 31 currently