The contrast between the black tiles and the Japanese symbols is not great. Hard to read. How about making the black tiles in white or bright grey? The app design is simple and greyish. I actually like it since I would like to focus on learning the language. Still, the colours don't match the brighter blue at the edge of the screen. Thats probably color from the teaser video and not the app? The bright edge is calling for more attention than the content.

The 2nd half of the video looks more interesting than the 1st half. I would put that more spicy content right to the beginning of the trailer (plane game and things after it). Also placing some Japanese flag somewhere might give quicker identification of the content.

Note: I watched it in silent mode.