The pink bar will quickly drain and instantly fill up for each hits on an enemy (multi-hitting enemies counts as individual stacks so you can fill the bar up really quickly if you do that). The blue bar will slowly be drained after the pink bar is fully drained, if you refill the pink bar, the blue one will slowly rise up again.
My strategy for this one is simple, really. Switch to Laser shot and dash through everything, when your pink bar is about to be fully drained, shoot 1-2 time. Fills up instantly.
If you're taking a bit too much damage, perhaps increase your defense stat.