We all are wondering what Ryokugyu (Green bull) is after in Wano. I believe that he neither wants to confront the pirates nor is interested in Wano itself. Instead, he’s after CP0. That is why he called them and told them to wait for him to arrive.
Ryokugyu was the one to fight the Revolutionary Army at the Reverie with Fujitora. Fujitora saw at Dressrosa what kind of despair the World government’s corruption brings upon ordinary citizens. The Revolutionary Army collected all the evidence of the World government’s involvement. Not talking about how that fight went, but I do think that Fujitora and Ryokugyu learned some hard facts about the World government.
The Marine higher ups dislike the World government (except for Kizaru, he doesn’t give a shit). Akainu just learned that there’s an entity (individual or group) above the Gorosei giving orders they follow; these orders turn him and his organization into a joke as they expect him to protect the pirates and corruption he is supposed to fight. Fujitora seems to be aligned with SWORD and must hate the World government for keeping up this corrupt and unjust world order.
While their motivation is quite different, both would want the marines to be a little more independent. They can’t just use force for that as the World government is quite powerful. But investigating corruption and arresting a few guilty henchmen? That’ll put some cracks in the World government’s system without causing too much havoc.
Now would the Marines use any evidence they gained from the Revolutionary Army? Akainu would decline as he wouldn’t believe his enemies. Fujitora may also decline since he couldn’t verify it. But Ryokugyu? The guy screams chaotic good/neutral from what we’ve seen. He’d just try confronting the dudes with the evidence for shits and giggles and let their reaction be his proof. That’s exactly what I’m expecting him to do:
Ryo: “Well hello there.”
CP0: “An admiral? Finally the reinforcements are here. Took you long enough!”
Ryo: “I tend to enjoy my travels and get lost in the scenery quite often, sorry.”
CP0: “We got orders to capture Nico Robin. Everyone else you can arrest or kill. Turn this lawless country into a wasteland to make an example!”
Ryo: “My, my. Someone’s on edge. Plans didn’t go so well, eh?”
CP0: “You might be an admiral, but that’s crossing the line. Don’t forget who’s feeding you.”
Ryo: “Haven’t eaten in the last 3 years, so I guess nobody’s been feeding me. I’d love for a beautiful lady to do so though. Do you happen to know one?”
CP0: “Are you making fun of me? You better start taking me serious!”
Ryo: “Relax. I’m taking you very serious, believe me. After all, I’m here for you.”
CP0: “For me? Explain yourself!”
Ryo: “Well you see, this pressing evidence caught my very limited attention, so I started an investigation of my own. That’s why I’m here now, not because of orders from above to support your super secret operation.”
CP0: “Does the fleet admiral know about this?!”
Ryo: “He obviously knows that I’m here to catch criminals, but let’s get to the point: Here’s some really nasty delivery lists and invoices signed by different CP0 agents – including you – and some beautiful pictures of you guys next to some really bad people of the criminal underworld. All of that seems awfully illegal.”
CP0: “W-.. We fulfill our orders. The WG’s activities aren’t of interest to you. We’ll inform you about the things you need to know and that’s that. Let’s get rid of Wano now.”
Ryo: “And here I was hoping you would just calmly tell me how everything’s fabricated and I could fly back home. But oops, I accidentally grabbed your mask and your face told me that it’s very much real. I bet the poor WG had no idea its henchmen did these terrible things, right? Seems like I have to arrest you now. How exhausting… ”
After that’s done, he has the Marines bring back the WG dudes to HQ and enters Wano undercover. After arriving he’s immediately invited to the big party by Luffy himself, because he appeared to be hungry. He thinks to himself: “You were right, Fuji. You’re really missing out on one hell of a smile.”
Theory by Jail_Chris_Brown (https://www.reddit.com/user/Jail_Chris_Brown)