World of Behemoths

Although the vast number of sea monsters dwelling in the depths of the Bone Sea had powerful strength and physiques, they were weak against attacks on their soul. 

Under Duna's soul suppression, the sea monsters couldn't bear it and fled.

Duna continued her descent without difficulty, shooing away any and every sea monster that dared to cross her path. 

Nevertheless, the deeper she went, the stronger the sea monsters appeared. 

At 10,000fts sea depth, Duna could only see Mid Arch Demon-level sea monsters as big as the human kingdom's palaces. 

At 20,000fts sea depth, she finds Late Arch Demon-level sea monsters as big as the street blocks in human cities.

At 40,000fts sea depth, although few in numbers, only Peak Arch Demon-level sea monsters of various sizes thrived. 

Furthermore, it was no longer a lightless world.