Hideo Kojima is very active on Twitter and, recently, he's been tweeting about the anime Made in Abyss. Kojima reviewed the show in a tweet, "Watched Made In Abyss up to Episode 3 as I was recommended by my staff. Took a while to get use to the drawing but setting of the abyss (big hole) and the world were very interesting. Still it was 'relic' to me and not quite 'trainee' yet. I may dig a bit more in deep." He then tweeted that he bought the whole manga series (likely in response to his staff member who said he should check out the source material.)

So what exactly is Made in Abyss? It was originally a manga written by Akihito Tsukushi and later adapted into a 13-episode TV series in 2017. Three films, Made in Abyss: Journey's Dawn, Made in Abyss: Wandering Twilight, and Made in Abyss: Dawn of the Deep Soul, were also produced. The last one was recently released in January 2020.

The protagonist of Made in Abyss is an orphaned girl, Riko, who lives in a town surrounded by a big giant hole called the Abyss. In the Abyss are remnants of a strange civilization and so-called cave raiders descend into the hole to bring back artifacts. Only there's one caveat (other than possible death by monsters in the hole): the deeper you descend, the more you'll be affected by a strange curse when you ascend to the surface again.