Jagei Hakkei translates to "Evil Welcoming/Inviting Eight Views". Ya is another pronunciation for the number eight in Japanese, being the kun'yomi or native Japanese pronunciation and reading of its kanji.
Usage See Special:Whatlinkshere/Etymology:Yakei for a list of articles using this term. This is an etymology page: a page detailing the origins of terminology used in the series in regards to real world culture and history.