The first guardian you fight is 'Ninja'. This isn't too hard, and you can beat it without getting hit.
Simply spam homing attacks and watch for the arms raising up. Before it strikes, hold
and
together to parry, and repeat until destroyed.
Here's some gameplay to show you what it's like:
You don't have to do it as I've described, but it was fast and I didn't lose the rings I'd just spent 10+ minutes collecting obsessively.