He ordered "the hit" but the kid who carried it out didn't know that, he was just some random teenager they hired from a suspicious website/text message. He likely knew the hit would happen at some point but how and by whom he couldn't have known about because his underlings handled that (the boss doesn't deal with the nitty gritty). The fact that he had a hot dog in the exact spot he just so happened to accidentally get stabbed in is the biggest asspull imaginable (let alone the fact that the hotdog was enough to stop a long knife from at least nicking him when the kid tripped and fell with his full body weight onto Ajiki).
Also Ajiki doesn't know shit about Okaya which is why he's getting bored and taking action himself. It's specifically because he doesn't understand him and why he's taking things so slowly, in a cat and mouse type of way, that he wants Okaya dead. The only thing he knows is that Maria is likely the culprit behind the other murders (because Okaya already figured it out with his L levels of deduction aka bullshit reasoning).
As an aside, this isn't really that much of a twist. The fact that Ajiki is the young master of a Yakuza crime family is definitely information I wouldn't have predicted but the fact that he's backstabbing Okaya isn't shocking in the least. They had already set it up for him to turn on him in previous chapters with the very obvious remarks about how Okaya isn't treating the deaths of his "friends" as anything more than losing pieces in a chess game. The main thing I'm concerned with is that Maria is distancing herself from Okaya in regards to collaboration with him but I guarantee she's going to take it upon herself to handle this and Okaya is likely going to do the same and they'll cross paths again where both essentially reveal themselves to each other.
My prediction is Okaya confronts Ajiki at the shrine and Maria confronts some rando from the organization at the same shrine and they see each other as they take out their respective enemies. Husband will also show up because he was monitoring Maria and catch both of them in the act. He'll take them both in but because Okaya's mom is the Chief his involvement will be swept under the rug so Maria is the only one getting caught out and the husband will have to make a choice on whether to help her or not from that point. Okaya essentially has her exactly where he wants her since she's in police custody and that is where the real endgame starts.