Depends.
How big is the Katamari at this point? If we're talking starting size, I just need a good pair of boots and a moment to get stompin'. Sure, stepping on that thing might suck, but the Prince is tiny.
If we're bringing him up to my size... That fucker can roll up a tank. Weapons would just add to the density of the Katamari. I'm taking a week to dig myself a hole to hide in, and praying it's deep enough to hide until he forgets about me, or he's so large he rolls up landmasses. At that point, we're all getting turned into a star.