i highly recommend reading the novel because it explains all ur questions(▰˘◡˘▰)
rifts and dungeons are different because im pretty sure dungeons are used for a longer period of time for resource gathering (if i remember correctly) and i lowkey cant remember about rifts, eui jae saves sa young before the rift and cares for him in hospital for a while b4 promising to come back after clearing it, sa young becomes a test subject after J leaves due to lack of hospital funds from Js ‘death’(≧∀≦) i hope this clears it up a bit!!

I am struggling to understand some parts, are rift and dungeon the same thing ? Can we use those 2 word in a interchangeable way ?? Also did cha eui jae save sa young before the yellow sea drift as J, before sayoung becomes a test subject ? Is that why sayoung says "I found you" ?
Alos can someone explain what is a dungeon erosion cuz I couldn't understand it ...