Lucy Morstan, the elder Morstan sibling, exhibits an androgynous appearance with fair chocolate brown hair and violet eyes, frequently leading to her being mistaken for a man. Her standard attire includes a white and red jacket layered over a black v-neck shirt, a gold locket necklace, a wristwatch, a mustard yellow belt, forest green pants, and long brown boots.

Stoic, rough, and physically inclined, Lucy contrasts sharply with her younger sister Mary's intellectual demeanor. She fiercely protects Mary, readily risking herself or employing brute force to secure her sister’s safety and happiness. Underneath this hardened exterior, Lucy conceals a heart of gold, clumsiness, and a hidden dorkiness. Hardworking and generous, she operates by a powerful sense of righteousness, though her initial interactions often come across as abrasive.

Lucy and Mary fled together to Kabukicho’s east side as youths, specifically on the day Mary was slated for adoption. This choice prioritized their familial bond and autonomy over separation, cementing Lucy’s lifelong role as Mary’s protector and companion.