I guess I was doing it wrong, as I ran from the red ones in the early areas because clearly I was going to get curbstomped on them. But the XP gain on Hard after doing "knock-down into all-out attacks" for Persona 3-4 is brutal.
Once I got in the upper areas (on Easy) the red guards weren't so bad as I generally had a weakness for them to be knocked down. But at that point I had no more SP.
Apparently, if you fuse a "Genbu" you can fight the Silky's (or whatever they're called. The women demon's in red dresses) that will Dormina/sleep you. If you get sleeped, you'll recover SP. And since they use Bufu, Genbu will make your PC immune. The problem is, you can't simply guard since they can't Dormina you if you guard. So you have to attack them. And they'll still damage you while you're asleep. It's a bit of a shortcut, but it may work.
And I only had like 2 of two different SP regen items for 5SP each. The vending machines limit those to 1 a week apparently. :'(