Would welcome other ideas for categories, here is a few I thought up / is obvious:

100% I think walkingeye is interested in this Low% No unnecessary pickups, this might have to be thought out if this is viable or not Spirit% Timer ends when all 6 spirits gained

If there is major differences in the difficulties, this can also be added.

Misc:

The minigame outside Airl's dungeon Boss battles? This would probably be a stretch without a boss battle mode (that's a shame!)

Feel free to support any of these ideas or provide your own, if there is a desire for any to be added we can go about discussing it.

100% is something I'm planning on routing and running, as soon as I either hit 1:29 at any% or if I plateau before then.

Low% is fine but I would not personally have any interest in running this category. I think you would end up with L1 of all weapons except the L3 heavy sword, 1 holy rod scroll, 1 earth sword scroll, 1 dark bow scroll, and 1 wind rod scroll. For the wind rod scroll, it's really hard to pick up only one of the two that drop from the chest where you get them, so maybe allowing 2 wind rod scrolls is fine. It seems like a pain to restrict rank. The whole thing just seems a bit tedious.

It turns out it's not too difficult to restrict your own rank artificially. The only forced healing is when you beat a boss, and you can time bombs such that you never actually hit full health so you never rank up. This makes Low% much more unique of a category compared to any%. That being said, I'm not exactly in a rush to run it, but I probably would take a few stabs at it sometime after getting better at 100%.

I'm interested in helping to route out 100% if help is desired. I would love to see a Low% run done but I agree it seems like it would be a bit difficult to route and even more tiresome to execute. Would you need to avoid taking damage on bosses before you acquire bombs or is there another way to avoid the heal on the boss before Dytto?

You would have to avoid taking damage until you get bombs. Tedious, but possible.

Help would of course be welcome on routing 100%! My plan was to compile the full list of items and their requirements. I think this list is close to complete: https://gamefaqs.gamespot.com/saturn/197768-the-legend-of-oasis/faqs/29754. Put those in a spreadsheet along with their requirements. If you want to take a stab at it or if you want to take another approach, feel free. It'll probably be another week or two until I start work on routing it out myself.