Shishido is Youko's childhood friend and a wolfman. Initially appearing as Shirou, an intimidating man with sharp teeth, upon seeing the moon(Or an image of), he transforms into Shiho, a busty charismatic female pervert. A second glimpse of the moon transforms Shishido back. Shiho is the dominant personality, and is aware of everything that occurs when Shirou is in control of her body. While Shirou has a crush on Youko and attempts to discover if Asahi is aware of her secret, Shiho is more playful and amorous, deriving enjoyment from being perverse. She often tries to force Youko into admitting her true feelings towards Asahi. While her father is also a wolfman, her mother is only shown in sillouette and is referred to as a "Charismatic Female Pervert".

Shishido Shirou (紫々戸 獅狼)
A wolf-man who is sent by Youko's father to see if she is keeping her secret at school. He also happens to have a crush on her.
All Animals Are Dogs: He reflexively jumps to catch a wooden stick that Asahi throws, despite being a wolf.
Kansai Regional Dialect/Antiquated Linguistics: His manner of speech is a strange mix of both.
Out of Focus: After a few chapters of introduction, he was largely relegated to the background and rarely appears compared to Shiho.
Perpetual Frowner: He constantly looks angry or annoyed.
Scary Teeth: Rows of very sharp fangs.
Unlucky Childhood Friend: He wants to marry with Youko, but she isn't interested. Him marrying anyone would be a bit problematic anyway...
(Source: Wikipedia, TV Tropes)