This is a trailer for an upcoming horizontal shoot ‘em up called Heaven Variant, by the three-man team at Zanrai Interactive. Zanrai has made it clear on their FAQ that the game will not be bullet hell, but nonetheless aims to appease both hardcore and casual players. It currently has no release date.
Note: this video was released in February, and since then the developers have made some changes to the basic game mechanics, including dropping mouse control for precise 360-degree aiming. In the latest trailer you can see that weapons now lock to a few set angles: