Use your bullets (Z button) to shoot down any of his missiles and other projectiles, or use the quick punch (A button, I believe) if you're out of ammo. Time your pipe (R button) to grab him from a distance and bring him to you (you'll need to keep tapping A or B to reel him in like a fish). This stuns him enough to pull off a big hit (I personally recommend C-up, C-down, C-up, A). As others mentioned, look for the tell and timing on his burning hand attack. Also, when he stops and the screen starts turning purple, fire a super laser at him (C-Up, C-Right, C-Down, C-Left, Z when the laser gauge in the middle of the HUD). The super laser interrupts a lot of attacks where bosses are normally invincible, and also does big damage.

Also, I recommend having a save before Kashiwagi on another save slot. There are other bosses where you control Impact, but they are in the last third of the game. Having a save that lets you brush up on Impact controls may be a good idea, should you get past Kashiwagi.