Kado: The Right Answer

Kado: The Right Answer (正解するカド, Seikai Suru Kado) is a Japanese CG animation television series produced by Toei Animation.The series first aired from April to June 2017. The episode zero, which tells the event before Shindō and Hanamori taking off on the plane, was exclusively distributed via Amazon Prime Video in Japan and Crunchyroll.

Plot
On a plane bound for their business trip, Kōjirō Shindō and his co-worker Shun Hanamori witness the sudden appearance of the Kado, a cube of 2km length, out of thin air landing and enveloping their plane. All 252 passengers including Shindō, Hanamori, and the flight crew members are admitted intact into the cube and they encounter a strange being within. This being assumes the form of a human man, identifying himself as Yaha-kui zaShunina, and he wishes to "advance the world".