Seikai Suru Kado

On his way back from a business trip, negotiator Shindou Koujirou witnesses a large cube appear out of thin air, which swallows the plane he was riding, along with all of its passengers. Inside the mysterious cube is a being in the form of a human man, named Yahakui Zashunina. He is from a place called the "anisotropic," and he wants to "advance the world."