Kogechibi is a tiny entity inhabiting the Great Library, resembling a four-inch-tall version of Eve but with distinct eye coloration. Her name derives from the one-eyed cloak ("Koge") that envelops her entire body, leaving only her eyes visible. She communicates primarily through unintelligible, baby-like sounds. Within the library, she functions as comic relief.

She originates directly from Eve; Kogechibi is a fragment that gains independent existence when Eve overexerts herself. The anime adaptation highlights her notable fascination with fireworks and explosives, during which she sometimes speaks recognizable words related to these subjects. Her narrative role remains largely peripheral to the main plot across official media. The visual novel further integrates her into the library's mechanics, where she is also affectionately known as "O-chibi-chan".