The Eternal Dark City

He was shipwrecked and drifted to an island, where he discovered another civilization hidden in the shadow of mankind. He was turned into another inhuman creature. Is this an advanced stage of human evolution or a vicious curse on life? This civilization is dormant, waiting for the time to come... And it will burst out. He will choose which side he belongs to between the two civilizations. Is there co-evolution between civilizations, all-out war, or is there a third way...? [There are manuscripts saved, but not many. Stable updates are guaranteed. ]