A sad fact, but as a rule, in case if an anime has no source such as manga or light novel, the odds are weak. Therefore, it's always complicated to discuss such a kind of anime since we have almost no data on which we might rely. Nonetheless, we would like to try to answer your question as much as possible.
Since we have no source for another television adaptation, the decision on renewal would mostly depend on two factors, namely, how the viewing audience responded to the series, as well as the BD/DVD sales of the franchise. Not less important is how many episodes are in the first season.
Fairy Gone Season 1 consists of twenty-four episodes. As a result, we are now talking about the double-cour anime series. In case of single-cour, we might hope that another round is planned by the P.A.Works studio. Yet in case with Fairy Gone, the studio announced a 24-episode installment. Unfortunately, such a decision doesn't play in favor of renewal since it's a very difficult process to produce the full season, which contains twenty-four episodes.
Another key factor which could affect the decision on renewal is the reception, which Fairy Gone has received from critics and viewers. Sadly, but Fairy Gone looks as a mediocre action series. On MyAnimeList, the anime holds a score of 6.15 based on over 11,000 votes.
Finally, to date we have no data about the BD/DVD sales of the franchise since the data will be available after Fairy Gone Season 1 concluded. Summing up, we doubt that Fairy Gone could have a second season. And even if we are wrong, the anime most likely should go on a long-term hiatus, once Season 1 is coming to an end. We would like to be wrong, yet in our opinion, Fairy Gone won't return for Season 2, at least in the foreseeable future.
Fairy Gone Season 2 Release Date
Even despite our forecast, we don't rule out that Fairy Gone Season 2 might happen someday. But when? It's worth noting that as a rule it takes at least one year to produce and promote the a full 24-episode season, if we have enough source material. In case of Fairy Gone, we don't have it. Therefore, it might take much more time to produce Fairy Gone Season 2. Therefore, in case of renewal, we should expect Fairy Gone Season 2 not earlier than in 2022.
In any case, all the data above is nothing but our forecast. We don't have any official data on the subject of renewal to date. However, as soon as the P.A.Works studio announces any news on the subject, we will update this page. So guys, stay tuned for updates. We will keep you informed.
Fairy Gone Summary
The story is set in the world which survived an epic war called the War of Unification. During the war, some soldiers were implanted with Fairy organs that allowed them to summon the fairy power. Those who possessed such superhuman abilities were nicknamed Fairy Soldiers. However, when the war is over, these soldiers remained purposeless. As a result, they were forced to use their power not on purpose. Some of them started working in the governmental structures, while the rest joined mafia or have become terrorists.
As a result, an organization called Dorothea has been created. The story focuses on Mariya, a new recruit of Dorothea, who is responsible in the investigation of fairy-related crimes.