Gunko might be the latest character who could come out as the traitor in One Piece, given her similar appearance to Kaola from the Revolutionary Army. However, despite this, she has yet to showcase any suspicious behavior that might make her a potential traitor. On the other hand, one Holy Knight might be under the radar for becoming the next traitor, and his Devil Fruit nature could be the key.
Saint Killingham might have awakened his Devil Fruit, given the smoke ring around his neck. However, unlike his other allies, Killingham possesses white clouds that tie him to the good side. Moreover, the model of this Holy Knight's devil fruit also ties him with the arrival of a new ruler, tying Killingham with the protagonist group.
Disclaimer: This article contains potential spoilers from the manga series and expresses the author's opinion.
One Piece: Exploring Saint Killingham as the Holy Knights' traitor

Saint Killingham is one of the supporting antagonists from One Piece's Elbaph Arc. The Holy Knight first appears in chapter 1140, alongside Saint Sommers, as both of them were summoned to Elbaph Island through the Abyss magic circle.
Immediately on his arrival, the Killingham had white clouds around it, meaning that his devil fruit might be in a state of continuous awakening. Saint Killingham ate the Dragon-Dragon devil fruit, modeled after the mythical Chinese dragon Qilin. The devil fruit allowed the Holy Knight to make anyone sleep from a long distance and manifest creatures from an individual's worst nightmares.
So far, until One Piece chapter 1144, Saint Killingham has yet to showcase any rebellious behavior toward the World Government and Holy Knights. However, it might not be long before Killingham rebels against his side and joins Luffy. Fortunately, there are various clues to proving Killingham as a traitor.

Firstly, the clouds that appear around his neck are white. As seen in the stereotype developed through the appearance of various awakened devil fruits, this color belongs to the good side.
Examples include Luffy's Nika fruit (Gear 5) and Yamato's Okuchi no Makami awakenings. On the other hand, Killingham's subordinates like Lucci, Gorosei, and Shamrock (sword) have black colored clouds, showcasing the nature of their devil fruits. So, Killingham might have some secrets.

Secondly, the biggest hint to Killingham's betrayal might be the model of his Devil Fruit. Qilin (the model of Killingham's dragon-dragon devil fruit) is a Chinese legend that only appears at the arrival of a new leader. Luffy, considered the successor of JoyBoy, who might liberate everyone, could be the reason behind Saint Killingham's arrival.
So, these hints suggest that Killingham might be looking for a chance to betray his comrades and join the side of the Straw Hat Pirates. Even though Gunko comes out more suitable as a traitor, when it comes to appearances, Killingham might be the true traitor of the Holy Knights.
Analysis and Final Thoughts
As already explained, Qilin appears on the arrival of a new leader. However, it also appears on the death of an already-present leader. The king in this case might be King Harald, who died 14 years ago, which isn't that significant of a time. So, to be on the safe side, take this theory with a huge grain of salt.
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