Like someone already mentioned, Kojima also reminds me of The Sopranos Richie Aprile. Not only in that he's an old gangster who spent a lot of time locked away and still does things the "old way" but also because of what the big man said, that Kojima can only get his rocks off when violence is involved with Richie holding a gun to his partner's head while doing the deed.
Ofc, this might be just seeing connections where there are none, but I wouldn't be surprised if the author did watch The Sopranos and took inspiration from it, especially since it is an exceptionally well done show.