An apocalyptic event has ravaged Japan, leaving nothing but endless sandy plains behind, and a strange rusting disease terrorizes the remnants of civilization. According to the government, the horrific state of the new world is the result of mushroom spores being spread by the likes of Bisco Akaboshi, labeled the Man-Eating Mushroom. But Bisco would beg to differ. In reality, he is a Mushroom Protector, determined to uncover the legendary Sabikui mushroom—said to be the ultimate cure for the rusting disease. Joining him on his quest are his giant crab Akutagawa and the kind doctor Milo Nekoyanagi, who is actively searching for a rust poisoning treatment for his sick sister. Despite the prejudice aimed toward him by the common folk, Bisco refuses to give up on his quest to purify the rotting world.

The Shadows, characterized by their pitch-black appearance and tendency to emit soot when agitated, are a family of nobles who reside in a colossal manor deep within the mountains far from other humans. When a Shadow child is nearly of-age, they are assigned a Living Doll who acts not only as their attendant but also as their second half—the faces they could have had if not for their complexion. Emilico is a cheerful, newly created Doll who serves a rather soft-spoken master named Kate. Despite their difference in personalities, Emilico does what she can to carry out the needs of her master. As she learns more about her role and duty, Emilico begins to meet her fellow Dolls and their respective masters and comes to know more about the purpose of her existence. Do not fret over trivial matters, says one of the rules by which all Dolls must abide. But how could the ever-curious Emilico do so in the face of the deep secrets that the Shadows House holds?

Narumi Fujishima may seem like a normal high school student at first glance, but in reality he is a pessimistic outsider. Due to his father's work, he had to constantly transfer schools, and thus he has never managed to become a part of society. When he is forced to join the gardening club by his cheerful classmate Ayaka Shinozaki, Narumi encounters the genius hacker Alice, who lives in isolation above Hanamaru, the ramen shop where Ayaka works part-time. He then discovers that Alice is running a special private detective agency, and that all her professional associates refer to themselves as NEETs: Not in Education, Employment, or Training. Joining the NEET detective agency due to his personal connection with a criminal case, Narumi finds himself entangled in a world of dangerous investigations conducted by the ill-assorted group of detectives, all the while trying to track down the crime syndicate which seems to have mysterious ties to Alice.

Third season of One Punch Man.