Kaishaku(介錯?) is a group of two manga artists consisting of Hitoshi Ota(太田 仁,Ōta Hitoshi?) and Terumasa Shichinohe(七戸 輝正,Shichinohe Terumasa?). The name comes from Kaishakunin(介錯人?), an appointed second person whose duty it is to decapitate one who commits seppuku - ritual suicide by disembowelment. Their anime also tends to have a happier ending after the credits on each last episode.
Since Kannazuki no Miko, the characters of Himeko Kurusugawa and Chikane Himemiya appear in the following Kaishaku projects: as Kuu (in personality and characteristics)/Himiko (in name, appearance and love interest) and Kaon in Kyoshiro to Towa no Sora, also as Tendo Hikaru and Utashiro Haruka in Hazama no Uta, in Himegami no Miko as Himeko Hinomiya and Chikane Kouzuki, in The Cross Triangle as Kurusu Ereshkigal and Kiraha Azaloth, and recently as protagonists in Zettai Shōjo Seiiki Amnesian.
Another recurring character is that of Ogami Souma from Kannazuki no Miko, who's also appeared as Ogami Jin in Kyoshiro to Towa no Sora, Ogami/Okami in The Cross Triangle, and as just Ogami in Zettai Shōjo Seiiki Amnesian.