Ryoko is from Tenchi Muyo, a huge anime franchise from back in the day. Very 90s. It aired on Toonami in the early 2000s which is where I and most other western viewers found it and fell in love. Since then it's developed a pretty hardcore fanbase.

Episodes 1-13 of the OVA continuity (Tenchi Muyo: Ryo-Okhi) are definitely worth a watch. There are 3 feature length movies too that are fun and cross into different continuities. It's a rare series insofar as it began as an anime, not a manga, so they kind of went nuts with different storylines. I also like the entirely separate manga storyline enough to have bought physical copies for my collection.

You can skip the other series, like Universe/Shin/GXP/anything post-2003 unless you're curious. There's a ton of it out there with so many spin offs it boggles the mind.

Sadly, the writing fell off terribly in later seasons (read became weird, incestuous and ends with a polygamous marriage... no thanks) and it became the personal vehicle for the original creator seemingly without any checks or artistic collaborations. It's aged, like a lot of older animes, but the original character designs are peak. It's also refreshing to watch an older anime without CGI (at least the early seasons)—there's something magical about cell animation and matte painted backgrounds.

It should have been rebooted by now, but the rights are so fragmented and the Japanese creators couldn't give a flying f*ck about the western market where the original series was always popular. Because of that it's practically unknown now to newer generations, which is a shame, but it's their own fault for sitting on an IP and not doing anything with it... or worse writing turgid self-referencing schlock that totally ignores the original characters that made the IP fun to begin with (personal rant).

That said, it's good fun and worth a watch!