Spending Experience

In about 2/3rds of all TTRPGs and 99% of Video Games, Experience lets you level up. That's it. Nothing wrong with it, but that's it. Kinda boring, if you ask me. Now, in Nexus, it ALSO lets you level up. But it also does more than that.

What does it do? Well, here's where it gets juicy.

The Level Up
Who doesn't like this one!? It's 100 experience to level up. But now there are other things to do with your experience, so it does need to be clarified, methinks.

Ability Score Increase
An ASI, just like the one you get from your class. These cost 25 experience. That's it.

Refinement
Crystals are an interesting thing. Seat of a creature's power, lets you do weird things like magic and all your other class features. So it shouldn't be surprising that you can do weird things with it. You can spend experience in varying amounts(Usually between 10 for basic things and 50 for cool things, but higher could also be done) to "Cultivate" blessings and other powers from within yourself, independent your class or other features. Just a thing.

Skill Points
Skill Points are technically sorta a weird specific type of training ish, but it's fine. By spending 10 Experience, you get a Skill Point to use just like when you made a character. 1 Skill Point nets you proficiency in a Skill or Tool. 2 Gets proficiency in an Ability Score's Checks. 3 gets proficiency in a Saving Throw, and 4 gets Expertise in a Skill or Tool. 5 will get Expertise in an Ability Score. 6 gets expertise in a Saving Throw. At seven, you can get triple proficiency in a Skill or tool. Etc.

Magic Item Creation
Now, ya don't need to spend Experience to do this, but you can. And if you do, holy hell, you can accomplish some shit. The best magic items, even including True Artifacts, can be made this way. It's basically putting your soul into your work. And like, I guess that ties experience points to the soul, or some shit... Don't over think this.

Ritual Improvement
Here's a weird one, which mixes in-character behavior with experience expenditure. Some rituals and other magical effects will do something huge and powerful, like permanently turn your character into a dragon or something. Part of the cost of these rituals is some of your Experience. Now, these might take anywhere from 10(Something like, a stat buff or gaining an extra racial feature, or some similar ritual) to hundreds(Turning into a dragon, etc.). But they're a way to do it. Of course, you do need to find a way to make it happen In-Character, just as much as Out-of-Character.