I find it curious that Queen only ended up developing such a plague now when a Devil Fruit user who utilises power similar to the Ice Oni Plague’s effects recently fell. Vegapunk in the past was able to isolate the powers of a Logia Devil Fruit and weaponise it. Queen could have potentially did the same with the Ice Oni Plague using a frost-specific Logia Devil Fruit user as a base i.e. the Yuki Yuki no Mi user, Monet.
All major powers within the New World are rushing to acquire resources and talents that utilises the power of science. Be it the Marines who have established the Special Science Group led by Vegapunk to fill the void left by the dissolution of the Shichibukai. Or Big Mom who planned a massive wedding to lure the Germa Kingdom in so that she could betray them and steal their cloning technology and scientific resources. Following along with that, it would make sense if Kaido had his own branch within the Beast Pirates that focused on weapons created by science and this is where Queen likely comes in. If Queen were part of the rogue research group Vegapunk and Judge (along with Caesar as the apprentice/assistant) belonged to in the past, it would help support Kaido’s confidence in his organisation and explain the lack of effort he has made to acquire additional scientific knowledge or resources.
Being a colleague of Vegapunk and Judge who discovered the “Lineage Factor”, it may explain how Queen was able to create his Ice Oni Plague Rounds. Similar to how Vegapunk isolated the properties of Borsalino’s Pika Pika no Mi and created the laser weapons for the Pacifista, Queen could have used his knowledge and research of the Lineage Factor to isolate the qualities of the Yuki Yuki no Mi and create the Ice Oni Plague Rounds. The Oni horns and aggressive tendencies could be a feature of Queen’s manipulation of the plague’s structure to create a weapon that has the capacity to completely eliminate his opponents when released.
The Ice Oni Plague Rounds seem like a recent development for Queen (none of the Beast Pirates have seen it before) and it’s qualities and effects appear to be comparable to Monet’s Yuki-Onna form. In the Yuki-Onna form, Monet takes on a beastly appearance with fangs, claws and an ice cold body that is able to freeze others through a bite/contact. The Ice Oni Plague infects the victim by freezing their body, eliminating their thought process and transforming them into an “Oni” with fangs, claws and horns. Monet’s Yuki-Onna form may not “infect” and eliminate the victims thought process through contact but there are enough similarities with the Yuki-Onna form that I can’t help but wonder. In Monet’s case, she has passive protection from the cold thanks to the Devil Fruit which allows her to both function in the frigid temperatures and to freeze her body when attacking her opponents. Without this protection, the user would eventually freeze to death when using such powers. Could Queen have researched Monet’s Yuki-Onna form and figured out how to recreate the freezing effects in a Plague Round?
As for why the Beast Pirates would have Monet; if the Big Mom Pirates had visited Punk Hazard (acquired a Centaur) after the Straw Hat Pirates journeyed through it, there is a possibility that with Jack in the vicinity, some of his forces could have also went to Punk Hazard. During the Punk Hazard Arc, Jack was tied up in Zou but he had subordinates not participating in the battle who were viewing the feed from Punk Hazard during Caesar’s “showcase”. Like the Big Mom Pirates, those Beast Pirates who were not participating in the battle on Zou may have visited Punk Hazard after Caesar’s defeat. While Caesar was no where to be found, the Beast Pirates could have procured Monet who was still alive.
The timing around the creation of the Ice Oni Plague Rounds and the similarities it has with Monet’s Yuki-Onna form (she was defeated almost a month ago in the One Piece timeline) has me very curious.