Setsuna

Japanese name:

セツナ

Is the Designer Child that plays host to the Planetary Gear known as Siren. She is the 7th member introduced and the last to awaken, assuming the leadership of the Planetary Gears upon her reawakening due to being part of the royal family.
Like Hana Mutou's pet Pitz, Setsuna is accompanied by her pet squirrel, Lappa.