Uff haha, that's really hard!
I managed to get to 10! I'd recommend a little less souls and an increased attack speed to begin with. That'll go long way I'm sure.
Then maybe some powerups would be a cool addition and I think the size of the firedot can be increased so that it's a bit more present.
That said though - looks very clean. It all seems to work as intended and it's an enjoyable experience. I think if I'd challenge myself I could get up to 15??
Thank you for sharing!