So with Areru now being aware there is a possible body snatcher or the Masaki's have a supernatural root after his visit with Katsuhito. Along with his knowledge of Ryoko and her current state, the cave and her body and his actions to fix that, how fucked is the normal Tenchi timeline?
As Arere is more likely than not going to act on something, be it if he fucks with Ryoko's seal, just ups and takes the Tenchi sword and frees her or has Katsuhito reveal more than he wants through stuff when Tenchi digs around about what is going on with his grandfather.
Since it kind of feels like we are about to see the premature kick off of the Tenchi plot, something that I wager could be really really bad if it happens considering Kagota is kind of a problem to deal with currently.
The only major divergences so far in the Tenchi Muyo! plot is Ryoko bonding with Areru and Tenchi finding out about his grandfather a bit early. The dominos falling right then aren't too severe, and actually might calm some things down. If Ayeka becomes infatuated with Tenchi, and Ryoko is infatuated with Areru, then those two might have a much calmer relationship this time around. It'll still be rough when Ayeka arrives to Earth, but past that, they have much less to fight over. (Side note, Ryoko being in love with Areru would also probably mean Ryo-Ohki would develop in that direction as well...)
...Now, if Areru is a little shit and tells Ayeka, "Hey, that's Yosho right there!" then it could cause some issues considering Ayeka was betrothed to Yoshi. Yes, they're half-siblings, and yes, their father wanted them to be wed anyways. Royals got to Royal. But Jurai has genetic engineering so the downsides to in-breeding is considered a solved issue, so it's not a taboo for them. I expect Areru to make fun of this practice endlessly, considering Ayeka is literally Tenchi's great aunt.
But Yosho doesn't love Ayeka romantically, only as a sister, and will probably try to let her down gently. He did so later when she found out, but she also thought he was actually as old as he appeared, fooled by the disguise field. So, it could be a bit rougher this time around, but will probably resolve about the same.
As for things that are about to happen... the timeline for Tenchi isn't concrete (Originally, it was believe to start in '92, so we'd actually be a year late into the Tenchi Muyo plot, but the later OVAs went with a sliding time-scale like how comics do so it's thrown things into question), but we do know Ryoko was freed in August, so if she is freed in the last day of June or into July, and this is the July right before that August in particular, then it's a month early. This can have some repercussions since Ryoko's Statute of Limitations doesn't kick in for another month, and her awakening is what ultimately gets the ball rolling for the plot.
Her wake-up is what gets Ayeka's ship to immediately head to Earth, as well as Kagato's. And Kagato's interest in Earth is what involves Mihoshi patrolling the solar system. So that's Ayeka, Sasami/Tsunami, Washu, and Mihoshi heading to Earth just because Ryoko woke up.
There's definitely some potential there for problems due to it being early. It's something that could cause a fight between Ayeka and Areru if he protects Ryoko... but if people just sat down and talked about how she was the mind controlled puppet of Kagato, the renown space criminal, then you could end that situation more peacefully. You'd just have to get through early-Ayeka's thick noggin. (I love Ayeka, please don't hurt her too much, Mr. Author.)
The
Tench-Ken will outright refuse to be wielded by Areru, as only those with royal Juraian blood can touch it without it zapping them. I don't think it would be as simple as an Alter-Self to fool it either. Since it's made directly from Tsunami herself and has three of Washu's gems embedded into it, it might even be semi-sentient? It's a
big deal for the upcoming arcs, and is as important a macguffin to Tenchi as the Silver Crystal is for Sailor Moon. Getting the gems is Kagato's primary objective coming to Earth, since he plans to use them to take control of
Tsunami-no-fune.
Even more so, if you give all three gems to Ryoko (and she's developed to the point of using their full power) she pretty much becomes the strongest non-god character in the universe, no doubt. She'd be stronger than
Z and could probably take on all the Sailor Moon villains at the same time. Being able to summon ten Light Hawk Wings is no joke.
After all that, the real dominos falling would be how the greater galactic community reacts towards Areru. If he defeats Kagato himself? He's going to get a lot of attention. GXP might send an officer to try and recruit him, a Jurai noble might try to adopt him if he keeps saying no to Yosho, someone might try to matchmake him with someone tied to Jurai in some ways... Things won't get more dangerous, but they'll definitely get more annoying as Galactic Politics try to interact with him as a major piece on the board.