First Appearance: Episode 1 - "Ideon Resurrected"
Final Appearance: "Be Invoked"

Sheryl worked extensively on the Sixth Civilisation excavations on behalf of the Science Academy, along with her father and Rouri. She was the only member of the archaelogical team left alive after the Buff Clan attack, and most of her time onboard the Solo Ship was spent trying to translate the Sixth Civilisation's language, and thus find a way to control the Ide. Onboard the ship, she served as an ersatz science officer, and was counted among the ship's senior crew. Initially she completely failed to get on with anyone and most of the crew saw her as a distant, slightly scary figure - especially the children.

Sheryl made little secret of her hatred for the colonists' fleeing existence, most notably when she led an escape attempt on a Karioka shuttle. She distrusted Karala long after the rest of the colonists accepted her, but eventually thawed. She became more friendly towards Cosmo, Bes and Kasha as well, though it would probably be a stretch to describe them as friends. Sheryl didn't really have any of those (she was even generally unfriendly towards her sister Lin), but tended to go in at the deep end and completely fall for someone. First of these was Colbeck of the Science Academy, who she quickly established a flirty interplay with, only for him to be killed by guards on Moonland. Soon after, her scientific interest in pooling her resources with Gije turned into love. However, the colonists' situation continued to play on her mind, and when her sister Lin was shot dead on Ajiba, she sank into depression and began to drink. Her state of mind worsened when Gije was killed in combat shortly afterwards.

When Doba sent the Solo Ship into the course of a comet, Sheryl took Lou up onto the deck of the ship, trying to invoke the Ide to save them all. The plan was a partial success as the Ide powered up the Ideon Gun and destroyed the comet, but Sheryl was knocked overboard by the feedback and died when her spacesuit ruptured. Her spirit was then reunited with her beloved Gije.

I was tempted to mention her flying frog admirer, but I was pushing my luck with the Rapappa entry already...