Thank you for the feedback!
The F key shouldn't need the shift key combination... hmmm. Could you please provide more details of your play environment? Platform: web (specify which browser), windows (specify version), linux (distro); Keyboard language and any other details you consider relevant.
The arrow flickering is caused by flying real close to the activation zone. You need to be flying above Calli's height and somewhere a bit below the top edge of the screen (when the camera zooms out). You can't down boost when you're too close to the ground or when you've sent chibiRyS off-screen. I'll probably add some sort of graphic to the game page to show the activation window.