World Seed SRD (WSRD) is intentionally built to be a pot you can throw a setting into, or reforge slightly so you can make any dish you want. And I'm working on the JJK setting right now, so we only care about pre-building the fantastic elements of the setting into World Seed, and the Jujutsu Kaisen universe only has 1
Cursed Energy
A pretty elegant addition to a world's laws, in my opinion. An aspect of reality that responds directly to the emotions of sapient and sentient creatures, capable of even giving birth to life itself. However malicious that life may be. Everything fantastic within the world Akutami-san has created, seems to flow from that, and these facts:
Cursed energy both comes from and responds to brain waves that correspond to negative human emotions.
It can be spent, no differently from electromagnetic energy, and interacts with matter similar to how light does. Being absorbed, refracted, reflected, radiating, etc
It can also coalesce into tangible matter, in high enough concentrations, made entirely from Cursed energy particles.
It seems to be some form of "W.I.M.P," on account of the fact it possesses all of these qualities, but remains invisible to most creatures and all but the most specialized detection tools. Likely absorbing all light outside of (or only interacting with) a very specific wavelength, beyond absorbing it.
So simulating it's behavior through WSRD means that cursed energy should -
Be present on all Character and Object sheets
Characters should have motivations that are related to a "curse" that colors their life. Some past, or ever present trauma that colors their existence
In Characters; standing Cursed energy levels should recover at a consistent rate based on their Stats (Rhyme), while the upper limit a Character can possess or infuse their body with at any one time should be controlled by another (Constitution).
In Objects; maximum Cursed energy levels should limited to that Object's Durability directly. But there should be a mechanism for determining an Object's progress towards "Cursed Tool" status, based on how often it's infused with Cursed Energy... It should probably be nearly identical to the way a body becomes permanently strengthened by cursed energy infusion, or the effects of Heavenly Restrictions that enhance the body.
Techniques just need to have a Cursed Energy cost attached, and that's simple enough.
Characters that are Cursed Spirits should exist first as a Character with a minimum personality and sentience (Motivation/Curse, REA, RHY). Then its current Cursed energy should determine -whether or not and by how much- it can manifest its physical form.
After all that is the Binding Vow, special laws that creatures can impose on themselves to control how their Cursed Energy flows and behaves overall. Usually by imposing a limit on themselves, in exchange for a boon. I think that's probably as simple as a Basic Action with a low cost, that creates an Event... Yeah, I think that's everything.
Now I've just got to put the numbers in after this mist has cleared....
