InuYasha (2000)

S1E21 Naraku's True Identity Unveiled

While on a date with Hojo, Kagome abruptly returns to the shrine after detecting the familiar aura of the Shikon Jewel shards. This leads her back to feudal Japan, where she learns from Naraku about his origins. He recounts how, fifty years prior, Onigumo was infatuated with Kikyo. Overwhelmed by the demons attracted to his darkness, Onigumo was consumed, giving rise to the demon Naraku we know today.