Chizuru's younger sister who works at the beachhouse with her. After Ika fails to invade the surface, she forces Ika to work for her to pay off a part of the wall she destroyed.
Running a beachhouse along with her two siblings, Eiko becomes the first human contact of the invading squid girl, Ika Musume. When Ika inadvertently damages the beachhouse, Eiko forces her to begin working there to pay off the cost of repairs, but she is unaware of how much a part of their lives Ika will come to be.
Eiko becomes the naive and eccentric Ika Musume's main guide to the world, as well as a foil who helps to keep her in line. While Eiko is often irritated by Ika's antics, or shows hostility towards her, she usually has the squid girl's best interests at heart and tends to look out for her. Eiko likewise plays straightman towards many of the series more oddly-behaved characters, which can sometimes make her seem abrasive or short-tempered, but it's probably more the case that she doesn't suffer fools gladly. She is almost unfailingly considerate toward the series more sensible and vulnerable characters, and gets along well with her siblings.
She is a childhood friendly of the lifeguard Goro, who she tends to tease playfully.