I'm glad to see Kira introduced as an ultimate goal for the protagonists. I've enjoyed the more one-off stories, but an overarching sense of direction is also welcome. Kira is such an effective villain because he breaks the mold. The worst Morioh has had to offer to this point are selfish individuals who would take advantage of others for personal gain. They'd take your money or hurt you, or steal pages from your face (you heard me), but they're not out to kill just for the sake of it. But Kira- he's a remorseless murder who kills for its own sake.
I said he breaks the mold, but you could also say Kira is a lot like other characters. Kira's just a regular citizen of Morioh whose lifestyle has been juiced up by the addition of a stand. The thing is that Kira just so happens to be a serial killer. But like Tonio or Rohan, he just wants to go about his stand fueled lifestyle in piece.
As much as a love the addition of Kira, it does throw a wrench into the flow of Diamond is Unbreakable. Josuke, Okuyasu, and Sigechi's get rich quick scheme is plenty of fun. But the whole time I'm reading this, in the back of my head I'm thinking "Really, Josuke? You're dicking around when you know Kira's on the loose". It's a tough situation. I'm tempted to say that we should just get all of the fun stuff taken care of before Kira is introduced. That way I as a reader can focus on the lighthearted fun without having more important stuff in the back of my mind. But I also wouldn't want Kira to be introduced at the end of the story. I want Kira introduced early, but I also don't want the gang to goof off while Kira is looming. It's a tough situation. Maybe some throwaway lines about Rohan and Jotaro working on the case while Josuke's out being a kid would've help.
But overall, it's not a big deal. I can usually put my concern aside. Shigechi's harvest was fun. Okuyasu and Josuke being greedy kids is always amusing. As was the back and forth of the lads using Shigechi and vice versa. Reminds me of Ed, Edd, and Eddy, of all things. Anyway, the scene at the bank stands out as one of funnies in Diamond is Unbreakable. The way everybody is trying to screw everyone else out of the money, even down to the banker, had me intrigued the whole way through.