Yayoi Hakudō serves as the Snake Knight among the Beast Knights, often seen in a white dress that complements her long platinum hair. Her animal partner, Shea Moon, encourages her to embrace her hobbies and feelings openly. Proficient in kendo, she wields a wooden sword integrated with her Domain Control ability, Flamberge. This technique wraps around her weapon to enhance its strength and cutting power. By connecting one end of Flamberge to her sword and the other to her arm, she extends her attack range, forging a unique fighting style that disregards conventional posture and leverages the sword's weight effectively.

Later, she duels Yuuhi Amamiya for the role of the second mythical beast knight. Victorious, she assumes the mantle of the Invisible, wielding the advanced technique Yorozukubi Orochi. This releases her domain as multiple ribbons that overwhelm and consume adversaries, which can merge into a single devastating lash called Senbiru.

Personality-wise, she exhibits a caring and motherly demeanor while secretly harboring a passion for manga and anime. She frequently cosplays as favorite characters but conceals this interest, fearing others' perceptions would shift. Emotionally, she develops feelings for Yuuhi after being rescued by him. Over time, she cultivates relationships with fellow knights, marrying Hyou Shimaki a decade after the final conflict and adopting the surname Shimaki Yayoi.

Her journey transitions her from a reserved individual hiding her hobbies to one confidently integrating passions and combat skills. Within the knights' collective, she contributes to group dynamics and participates in shared rituals, such as mourning fallen comrades by wearing black attire.