Chaika and her twin sister Pooshika are identical twins from Russia. Chaika is the twin in blue with glasses, while Pooshika wears red. The two girls fight with Project Blue in order to earn money for their ill father's medicine. Pooshika is bolder and more daring than the cautious Chaika, who tries to keep her in line. Chaika seems to be the better fighter of the two.
Both girls are blonde and wear their long hair in ponytails; Chaika's ponytail hangs to the right side of her head, and Pooshika's hangs to her left. They wear traditional Russian-style outfits with caps, white shirts, black vests, and colored skirts and boots over white pants. Both have blue eyes, although Chaika wears glasses while Pooshika does not.
Chaika's name in Russian (чайка) means "sea gull." She is named for a Russian restaurant in Shinjuku, Tokyo.
After the twins defeat the final boss, Lord River-n-White tells them that he's given the financial reward to another pilot, leaving the girls no money for their father's medicine. Angela appears and suggests that the twins become music stars, but she puts them to work as janitors instead.
In two-player mode, the twins fight with Whity the dolphin. They admire Whity's flying abilities, and although he gets tired of the twins' bickering, overall the three get along well. After the final boss battle, Chaika and Pooshika spy on Whity, trying to figure out how he can fly a plane. To their amazement, he takes off his head, revealing himself to be Captain Silver and Flint in a dolphin costume! But when the girls ask, "Really?" the game declares, "Well, no, not exactly," along with the images of two Martians. This enigmatic ending is never explained.
One-Player Mode Endings:
- Boss battle with Pandora or Gurabura: The twins are shown trying to decide how the game should end. Pooshika prefers the ending to show the girls exhausted from defeating all the enemies, while Chaika suggests that they should fight a mob instead.
- Boss battle with Lar or Do-ni Revision: As in their single-player ending in Sonic Wings 3, the girls try to get their payment from Lord River-n-White and instead end up cleaning for Angela.
- Boss battle with Balbi or Osaru: The twins return home to find their father up and well. When he reveals that he only had a hangover, they promptly clock him over the head with a Russian doll.
Two-Player Mode Endings:
- Boss battle with Pandora or Gurabura: Chaika and Pooshika ask Volk about what he'll do now that he's had his revenge on the enemy; Volk sarcastically replies that he's going to open a candy store in Pakistan. When the girls don't understand, he warns them not to play with fire then storms off. Pooshika still has a crush on him, but Chaika's just annoyed.
- Boss battle with Lar or Do-ni Revision: Pooshika challenges Volk to a fight. . . and ends up losing, naturally. Despite her loss, she vows that she'll win the next time, even though Chaika scolds her.
- Boss battle with Balbi or Osaru: As before, Pooshika challenges Volk to a fight, but he tells her to quit annoying him. Volk pulls a disappearing act that freaks the twins out so much, they pass out, and he makes his escape.