I don't think you can call him an assassin since he never killed anyone. The whole plot w his family was so bizarre as well like I didn't really get it, cos okay his brother protected him during a job gone wrong? (Why did he let his baby brother try in the 1st place?) Also bc the brother died the dad killed the mom??? To cover the kids being assassins? And then he just let's his son go cos it's his son idk the rest of the story is quite nice but I got stuck on this part a lot so I couldn't enjoy it properly. Lovely art tho.
Kimi no yoru ni fureru