Crosso.

Skeleton is a warrior and former assassin from the X-tail gender band.

Previously, before serving as a servant to the southern princess, Dreamtail, also a genderbent of Princess Dreamily, she served as an assassin for her younger sister, Princess Nightmet, but the latter turned to the dark side and continues to rule the northern side of the kingdom. Nightmet ordered her sister's death, but Crosso was unable to carry it out.

Crosso is friends with Epica from the Epictale genderbender, as her mother and Epica's mother are political allies and friends, although Crosso X's mother, Gastilda, has ambitions to conquer all worlds and subjugate them by treaty, with the exception of Epictale. Epica's mother, Epictale, Gastilda, secretly tries to stop her plans. Epica herself is the commander of her world's army, which belongs to her mother.

Besides them, Crosso has a full younger sister, X-Patricia, who supports her because Crosso also disagrees with her mother's plans to conquer other worlds. X-Chara, who was created by X-Gastilda as a biological weapon and is X-Chara's sister, Z-Frisk, also disagrees with the invader. However, X-Yrisk obeys X-Gastilda verbally. Essentially, X-Chara and X-Frisk are like half-younger sisters to Crosso and X-Patricia.