An additional part of Genma Taisen, serialized in Tokuma Shoten's Ryu (the predecessor to the modern Comic Ryu). Ryu was named after Ishinomori's Ryu trilogy, and this was done to commemorate its launch early on.

Vol 1-2 Subtitle: The Sound of the Eve of Myths
Vol 3 Subtitle: The Sound of the City of Skulls

(from ebookjapan):
Following the last part of "Genma Taisen", the work depicts a future world after the doom of the moon has fallen. ──── Humans living a primitive life...the "hominids" were ruled by the Ma. One day, one of the newborn human twins is taken to the Ma's castle and grows up as Roof, a Ma prince. Meanwhile, the remaining baby, Jin, awakens his supernatural powers when his mother is attacked and ......? The final manga version of the series, which has also been made into an TV anime series and is filled with Ishinomori's thoughts and feelings, was in Ryu!