So I happened upon an interesting find that there was a Langrisser I manga released in the 90s. At the very least I've hadn't ever heard it before, just the Langrisser III one.
It's from a Sega Magazine called Marukatsu Mega Drive (マル勝 メガドライブ), which ran for about a year before being superseded by another magazine. But evidently, in its first issue, it had a Langrisser I Manga called, simply enough, Langrisser Gaiden (ラングリッサー 外伝). From what little I've been able to find it centers around Talyor and that's really all I've been able to find.
I did locate a tweet, (which I should have saved, but didn't think too and now can't seem to locate it), but it did show some of the art (which is below). However, I can't seem to find any scans of the magazine and it doesn't seem SegaRetro has even begun to scan this particular magazine yet.
I don't know how hard it would be to obtain or if even if anyone really cares, and I'm not holding my breath that it might get a quick fan-translation, but I figured hey it's always interesting to see other Langrisser stuff and if someone knows anything more about it, it'd be neat to know.