The Morose Mononokean Season 1 Episode 2

The Ant

Ashiya uses his newfound sight to help remove a yokai attached to a classmate, but finds that it was a small part of a larger swarm as they later chase him around the school. The small yokai overpowers Ashiya and takes him to their leader, known only as "Big Boss Scree." Abeno was tasked to help them out by opening a portal to the underworld, letting the Scree swarm go first. Due to the parasite that is stuck to Big Boss, he is unable to go through the doorway. With Ashiya's encouragement, the Big Boss takes a specialised pill that will weaken the parasite. Big Boss Scree survived the extreme, possibly lethal, pain and was separated from the parasite. Alas, it fit through the doorway, reopened by Abeno, and 'exorcised' with the rest of the Scree.