How the hell does Captive Sun work.

I tested it out in practice range, and after I use the move, it seems i need to shoot the enemies in order to make these orbs grow bigger so they explode and do massive damage, but whenever i try it out in a match I'm not given any time to actually set up the move, and the orbs which i need to shoot disappear in like 2 seconds even when there isn't a Kiriko on the team. I could catch 3-4 people with the sunrise, yet none of them come out unscathed because the moment they are hit the orbs disappear and I seriously don't understand why. And the thing is, sometimes it does work, and I'm able to kill one person with my ult, but the moment I turn around to kill the next enemy player, even though the orb was still on them, suddenly the orb is gone even though it had only been 2 seconds since I used the ultimate.

I don't know how this damn thing works. Does it rely on sight or something? Is my game just glitching? Is it somehow being canceled? I genuinely don't know.