September is a combat android and one of Marciano's Twelve Sisters, functioning as both a personal hit squad operative and surrogate daughter to Madame Marciano. She displays an impulsive, overconfident personality, frequently taking reckless risks during missions to outshine her siblings—driven by a desire to prove herself and win Marciano's approval. This tendency culminates in her demise during Episode Three when she launches a solo helicopter assault against overwhelming opposition.

Her appearance mimics a late-teen young woman, standing 5’5” with a heavy android-built frame. She has straight brown hair with bangs, bright blue eyes, and dons a traditional maid costume in white and black with red trimmings, bows, white stockings, and black shoes. A small white hat, fastened by a thin black ribbon, tops her ensemble.

In combat, September wields an M14A1 rifle with a fixed bayonet, utilizing enhanced strength to handle the weapon effortlessly. She demonstrates exceptional marksmanship, achieving feats like three consecutive headshots while parachuting. Tactically versatile, she engages in long-range sniping and close-quarters combat but favors closing distance on enemies. Her skills include Jukenjutsu (bayonet martial arts) and Jujutsu, employing sacrifice throws and acrobatic maneuvers. Notably, she blocks melee attacks and evades explosions but never lands a bayonet thrust in observed engagements.

As an android, September shares standard sister-traits: enhanced physical capabilities, internal radio communication, and resilience to small arms fire due to armor plating, though vulnerable to heavy weapons. Her loyalty to Marciano is absolute, operating under April’s field leadership in their hierarchical command structure. She undergoes no significant character development before her early demise and appears exclusively in the main series.