Female / 168cm / 13 years old A-002 A test subject at this laboratory.

She is energetic and kind like a child, but also has a timid side. Her behavior is subtly cute, and she loves playing pranks, often teasing other subjects or researchers. Of course, they aren't malicious pranks. She has a subtle obsession.

She has brown bobbed hair and brown eyes, and unlike other subjects, her face looks relatively normal. She is always smiling. Her skin is paler than a normal person's. Her right arm is covered in something black and shaped like a large thorn. Her left arm is also covered in something black, and her fingertips are sharp. She wears a standard subject uniform—a thin, light gray (almost white) long-sleeved shirt with the right sleeve rolled up. Her pants are thin, faded blue long trousers.

They arrive at sunrise and leave at sunset—this is part of the researchers' rules. They are somewhat kind to Sky because of her bright and cooperative personality. They remain indifferent to Sky's pranks. Some researchers drink coffee frequently.

A tree inside a cylindrical glass container in the center of the laboratory's first floor. It is white with sky-blue leaves, and a black gem is embedded in the center of the trunk. It lives on blood, but no one knows who provides it—in fact, they aren't even sure if it's being fed blood at all. Because it consumes blood, some leaves turn red; A-178 sheds these red leaves itself once a month. Being a tree, it cannot speak, but if you listen very closely, you can hear a faint humming sound and something like a heartbeat.