556 is a quiet girl who is always teased by everybody, but for the reason that she is loved by everyone. Everyone skips to her lovely tune as she has the trumpet as her specialty. However, her luck was always bad, as she met a tragic end in a battle with the Black Witch. She was the latest style of weapon, unique in the Sisters' Cavalry, which had a strong tint in the honor guard. 556 was in charge of the squad fire support, and shot not to kill, but to protect her allies.
556 has the same military outfit, red eyes, and bunny ears and tail as the other Siesta Sisters. She has short, black hair. Some parts of her outfit have a purple color scheme.
- Member of the Siesta Sisters Imperial Guard Corps
- Subordinate of Siesta 00
- Comrade of Siesta 45
- Comrade of Siesta 410
In Alliance of the Golden Witch, Rosa Ushiromiya took one of Maria's ceramic bunnies and smashed it onto the floor when she abused her after she had returned from her shopping trip, in the weeks before the family meeting on Rokkenjima. Considering the fact that Maria spoke of her mother's bad side as the "evil witch", that Rosa was in that state of mind when she broke it, and in Twilight of the Golden Witch, it is indirectly confirmed that the bunny she destroyed was, in fact, Siesta 556.
- Just like the other Siesta Sisters, 556 is also named after a firearm round, here being the 5.56x45mm NATO assault rifle round.