Kai 解 (which means "to untie", and figuratively, "solution") is the collective name for the answer arcs (5–8) that "solve" the mysteries presented by the question arcs (1–4). Together, those 8 form the initial, complete story.

Hou 奉 ("to present") is the name for a new release of the series that includes the initial 8 arcs, plus the fandisc Rei 礼 ("gratitude") and three additional arcs not released before in VN format. These were all released together in one package by 07th Expansion back in 2014, but MangaGamer is taking its sweet time to getting this translated version out.