Awesome Idea Yo.
I wanted to get in on this but just had an operation on the meaty muscle on my right thumb on Friday, so my sketching skills are probably sub 50% at the moment.
My idea is a multi-directional super soaker with a four way trigger. Pull normally to shoot forward, press forward to shoot back and then left and right to shoot those ways. I was thinking a full arm sleeve with jets along the left and right of the forearm and then the forward one like spiderman’s web shooter and the back one coming from the elbow, maybe with a belt tank system.
I’ll have a go at sketching it the day of the submission. Maybe left handed 4th grader sketching. 
Is the deadline midnight on the 31st, US eastern time?