Yuika is a young child who has dark hair and dark-colored eyes. Her hair is styled into a small ponytail at the top right side of her head held by a ball ponytail holder, similar to Mayu Suzumoto. She wears a dark red dress with white ruffled socks and black Mary Janes.
A lively girl, Yuika seem to enjoy playing with insects. It is hinted that she plays with them by stabbing them with a stick. Yuika also likes to play games whenever she visits her grandfather, such as playing hide-and-seek or dress up, seemingly unaware of the lewd intentions of her grandfather.
Yuika makes a short appearance in chapter #09 from Corpse Party; Musume 2. She is sexually abused by her grandfather, the Principal of Kisaragi Academy Girls' School, under the guise of playing games such as dressing up whenever she comes to visit him.
Yuika is first seen making a burial for a praying mantis she affectionately names "bug-san" when she is approached by a girl in white. Then the scene forwards to the Principal visiting his office and notices the lights are off. Then he hears his granddaughter suggesting that they play hide-and-seek with him being "it."
After the Principal catches Yuika, he realizes that his granddaughter is actually Sachiko pretending to be her. He demands to see his granddaughter. Sachiko then display the corpse of Yuika who has a large stick protruding from her left eye. Sachiko states that since Yuika "loves to play with bugs," she had done the same to her. After she kills her grandfather, Sachiko puts on her dress.
Significant plot details end here.
Sachiko takes Yuika's dress after she kills her grandfather. As seen in colored pictures of the manga, Sachiko wears a red dress, so it's assumed that Yuika's dress is also red.
She is pretty cruel towards insects, seeing as how she enjoys stabbing them with sticks.
This might've been the reason Yuika was killed by Sachiko, who might've not seen a difference between killing a human and killing an insect.