Hakaba is an aspiring field linguist who specializes in the communication systems of monsters. After his professor injures himself in a hot-air balloon accident, Hakaba suddenly finds himself putting his knowledge to good use as he ventures into the Netherworld to pursue his professor's research. Upon arrival in his first village, Hakaba meets Susuki—his professor's half-werewolf half-human daughter. After adjusting to the environment's conditions, the two begin their journey to their first destination: the Cave of Goblins.

Heterogenia Linguistic: Ishuzoku Gengogaku Nyuumon follows the journey of Hakaba and Susuki as they traverse the Netherworld, documenting the languages and customs of every creature they come across.