sairei no hebi
(English: Snake of the Festival)
The ultimate villain of Shakugan no Shana and anime's biggest walking spoiler. Basically the Satan of this series' mythology, the Snake shows up in the third season... in the body of Sakai Yuuji. Shana and the rest take this about as well as you'd expect.
This tag is used for the Snake either in Yuuji's body (distinguished from his usual look by long hair) or his real body (a huge black snake).
