KEIYA is a writer who has authored many analysis guidebooks related to Ryukishi07's works and has featured in many interviews with him.
07th Expansion-Related Books
- Final Thoughts on Higurashi no Naku Koro ni
- Final Thoughts on Umineko no Naku Koro ni: Witch Hunting for the Episode 1-4
- Final Thoughts on Umineko no Naku Koro ni Chiru: Answer to the golden witch Episode 5-8
- Ryukishi07 Interviews
- Higurashi analysis columns on Seikaisha's light novel website
- Prefaces and notes on republished Toratsu and Faust interviews