Millis Steel, daughter of master thief Argus Steel, partners with him to seize the mythical Diancie and harness its diamond-forging powers. Masquerading as an ally, she aids Diancie’s escape from rival hunters while covertly tracking the group to advance her father’s schemes. Her trusted Chesnaught serves as both protector and enforcer, neutralizing threats with Vine Whip and Pin Missile.

Though cast in an antagonistic role, Millis weaves self-interest with unexpected compassion. She intercepts threats to Diancie and confronts the destructive Yveltal directly, stalling its rampage to enable others’ retreat. Her bond with Argus adds depth to their criminal pursuits—each prioritizes the other’s survival, exemplified when Argus shields her from Yveltal’s onslaught.

Her arc culminates in a decisive break from crime. After Xerneas halts Yveltal’s chaos, Millis and Argus abandon theft to reinvent themselves as confectioners, running a modest chocolate shop. This peaceful retreat frames their journey as one of atonement, contrasting prior ambitions with humble stability.

Sporting neck-length green hair, blue eyes, and a cropped black shirt, Millis navigates interactions with calculated charm, blending pragmatic cunning with flashes of playfulness. Strategic and resourceful, she deploys Chesnaught’s abilities with precision to outmaneuver obstacles.

Her arc remains anchored solely within the film’s timeline, driven equally by filial bonds and profit. Yet their quiet confectionery trade underscores a thematic focus on renewal over retribution, closing her story without expansion in other media.