Finally got it to work.
- Downloaded the PSO2 launch tweaker from Arks-Layer, set it up, and let the game update and launch through it.
- Ran the option to troubleshoot permissions issue with Gameguard
- Closed Nahimic audio as Fezix93's advice here https://forum.pso2.com/topic/3403/the-game-app-won-t-open/3.
- Prayed to Sweet Baby Jesus that it'd work
Hopefully it still runs tomorrow. Not even Bethesda games are this much of a headache. @John-Paul-RAGE Part of what makes the whole thing so frustrating is that there IS NO error message when this happens to people. The game just silently crashes before it even launches. The only reason I knew to try the troubleshooting option in the tweaker launcher was because unlike the regular launcher it actually says "Hey, you clicked start game and the game ain't started. Try running the repair Gameguard under the troubleshooting menu." If I were Sega I'd take a look at the third party launcher and learn a thing or two from them.