Even though I wrote this review for OVA II, it also applies to OVA I.
I learned of this OVA thanks to a video documenting Akiyuki Shimboh's works before working with Shaft, and somehow this interested me. I thought I would just appreciate it for some beautiful Shinboesque scenes and not much substance. Imagine my surprise that it's actually a good anime.
Yamamoto Youko is a high school student who was recruited in the 20th century to fly a space fighter. Even though she's just good in video games, her skills are immediately transferrable to flying space fighters.
She's a Mary Sue, but you'll like her in spite of it. She's a fun character.
It is said to be an isekai, but it's technically time travel. Yohko and her friends travelled 1000 years into the future. It features advanced technology rather than the usual isekai world of medieval Europe as seen in Escaflowne (old school) and numerous isekai nowadays. (Speaking of Escaflowne, the seiyuu for Yohko is the same seiyuu as one of the antagonists in Escaflowne, namely Dilandau.)
Two factions, Ness and Terra, are fighting for supremacy. But there's no death involved as the pilots are teleported back whenever their space fighter is destroyed.
There's no plot here, at least in the OVA. (Perhaps there is in the TV series.) It's silly if you think about it, but that's the point. It's not a serious anime where the stakes are high, where failure of our heroine means it's the end of the world. It's just a fun show with a fun character named Yamamoto Yohko. It's not a masterpiece by any means but good enough to be worth watching.