Shikieiki was the "Extra stage" boss for PoFV, the perpetrator, who is normally the sixth stage boss is Komachi.
Excuse me, but what are you talking about?
Shiki Eiki is everyone's final fight, apart for Shiki herself (who went around punishing everyone else for not listening to her lessons) - half the characters fought Aya then Komachi; some fought Aya then Yuuka, and a few others fought Yuuka and Komachi (not necessarily in that order). Every final stage (stage 9) for every character apart for Shiki Eiki is Shiki Eiki, who lectures the character and puts them through a trial. If they pass, you see the ending. If they fail, she'll repeat herself until you can pass.
