Upclose and Personal : Cold Steel
Steel is NOT your average low-life thug... unlike Gila and Diesel, he is second only next to Karst himself. That is, he takes his orders directly from the big boss. Since Karst has a certain Public image to maintain, Steel is often the one left in charge of handling all of Karst's 'unofficial transactions'. This is no small task, because going by Karst records, we may be talking about a pretty big 'department' here.
So it must have been quite an achievement for Steel ~ for Karst to trust him with such an important position, he must have proven himself to be quite the loyal follower. ( Of course Steel isn't stupid. He probably knows that getting into Karst's 'good books' meant he is the next in line to inherit Karst's fortune. Although one does wonder if he ever feels threatened by countess Mayhem's presence...)
And being Karst's right hand man does have its benefits. He gets to have his own personal goons under him at his beck and call, and as for the menial tasks he justs leaves it to the likes of Diesel and Gila. ( no point getting your hands dirty when you can get others to do it for you.) He's pretty much a 'boss' in his own right, so it's a pretty good deal .... that is.. until things get screwed up.
Still.. Steel is as important to Karst as Grognard is to Lupin. Lupin's interference may get Steel into trouble with his boss, but nevertheless, he is still Karst's best bet and probably the most dependable as far as your low-life mercenaries go.