The Fairies' Homecoming

The Fairies' Homecoming is the third story arc of Humanity Has Declined and features as episodes 5 and 6 of the anime series.

Summary
At the beginning of the story, a mysterious tablet appears outside the village that has no, apparent purpose. Later on, as The Human Monument Project moves forward, a festival is prepared in the village using a newfound source of electricity. While the townsfolk are excited, The Mediator learns that the local fairies are quickly fleeing the area because electromagnetic waves kill them. They leave behind a manual, however, explaining that a lack of fairies in the area makes accidents and misfortune more likely, whereas a density of them can cause impossible streaks of luck. During the festival, The Mediator sees a curious girl wander the village and accidentally draws her attention. This girl introduces herself as Pion and claims she is in search of her companion, Oyage. The following day, The Mediator and The Assistant are ordered to explore a building in the ruins of a city, where they wind up trapped and lost. As resources begin to dwindle, a good luck charm received from the leaving fairies earlier turns into a complete fairy, who offers to lead them to water. Instead, they find another tablet like the one outside the village and are attacked by slimes. After fending off a slime with the tablet, a robotic dog appears to attack the party instead. However, Pion appears and defeats the dog.

With Pion now in their party, traversing the labyrinthine building becomes a lot easier. That is, until they run into Oyage, who has similar powers to Pion and attacks them with giant machines and eventually transforms into a giant cat. By having the fairies and Pion cooperate to attack Oyage with a giant microwave, they manage to defeat his cat form. The waves from the microwave, in turn, start up a restore function in Oyage that returns his' and Pion's memories, revealing they are Pioneer and Voyager, two deep-space probes given humanoid form. After leaving the building and returning to the village, those working on The Human Monument Project rejoice over the possibilities this discovery offers. However, Voyager reveals that he was scared of the vastness in space and does not want to return, which is what the UN intends for them to do. Pioneer objects, only to burst into tears when Voyager reminds her that she too was frightened. This convinces The Mediator to sabotage the generator, preventing the UN from refueling Voyager and Pioneer. As punishment, she is interrogated and her hair is cut off.

In the end, she ends up spending the last bit of power Voyager and Pioneer have within them to create a wind-up system with a crank, which grants them just enough power to walk around for a minute when it is spun for a whole hour. Voyager and Pioneer are then stored in a cabinet when they return to their tablet forms.

Trivia

 * This storyline alludes to the Pioneer Anomaly that was first noticed in 1980. In short, this concerned an incident where the Pioneer spacecraft accelerated less than predicted. This was investigated and, as of 2012, it was revealed that the anomaly was perfectly explainable if all factors were taken into account.
 * This storyline is heavily tied to The Fairy's Secret Factory, as it introduces The Director who appears in that episode and reveals why The Mediator had short hair at the beginning of the show.