Martianman69

Inuyasha is not an isekai, it's time travel. She herself has gone through a time vortex that transported her from modern Japan to feudal Japan. What explains the demons and monsters? As society modernizes the source of demons and monsters weakens. This source is nature itself and human belief, the more nature and the more people believe then the likelier it is for these beings and even the abilities to exist. As things modernize and science takes root the demonic and holy presence of the supernatural weakens as the denser and more disbelieving the population becomes.