Maybe Drake will ask Aramaki to stop? Maybe Aramaki is in sword too. Drake has to leave Wano somehow.
idk, Drake did basically nothing for the alliance. He failed to stop CP0 from reaching rooftop.
So maybe this will be the pay off?
Or maybe Momo knows where is Pluton and will offer Aramaki an ancient weapon to leave Wano alone?
Maybe Onigashima is Ancient weapon itself? It would explain why Kaido wanted it transferred to Wano for no reason and that thing Marco mentioned for no reason.