Changing the difficulty will reset the level.
Heart Horror is a bullet hell shoot-em-up game. Your avatar is a lot larger than your hitbox - enemy bullets may touch your ship and yet you will not take damage. Only if the bullet touches the very centre of your ship will you lose a life point.
The core of gameplay is to avoid bullets, partially by recognizing and remembering enemy boss attack patterns.
Now go save the world from the Vast Horrors, okay? Thanks.