Ginga Ojousama Densetsu Yuna: Kanashimi no Siren

Both are short, stupid, obscure comedy series about fighting mecha-ish girls. Similar style of humor and similar characters and genres. 

Both are short OVAs adapted from games, in which the main character is a young girl who's treated as an idol by everyone around them because of things they did before the OVA's events (stuff you're half expected to know from having played the source games), and have a fair amount of CGDCT elements as well as Mecha battles. Both series also have a sizeable cast of supporting characters who unfortunately don't get enough screentime. 

Both are 90s OVAs that star cute girls in power armor, alien invaders attacking Earth, giant robots, and a lot of ridiculous and sometimes tongue in cheek humor. Although both are pretty lighthearted, Gran Doll gets notably more serious, but it's hard to tell if it's actually being serious or if the seriousness is part of the joke. 

Both are short OVAs following an adventures of good-natured but ditzy female protagonists, with a heavy serving of over the top and ridiculous 90s anime humor. Despite Detatoko Princess being fantasy and Yuna being sci-fi, both have taken pretty clear influence from magical girl anime 

Mahou Shoujo mixed with Mecha is a rare thing but these two anime are examples of such. Metal Fighter Miku has only transformation sequences while Ginga Ojousama Densetsu Yuna is Mahou Shoujo at its core with some elements of Mecha added in. 

Mahou Shoujo Mecha anime are a rare find and those two anime are examples of such. "Ginga Ojousama Densetsu Yuna" is a more classical Mahou Shoujo with strong Mecha elements. "Magic Knight Rayearth" is an isekai anime set in a fantasy world that slowly transforms into Mecha. 

Both series have old school style comedy humor, with a bit of action thrown in the mix for good measure. They are overlooked series that shouldn't be missed! 

Goofy humor, anime sci-fi, and space girls. Has that old school anime feeling. 

If you've ever wondered how did Yuna befriend everyone by fighting against them look no further - Nanoha tells exactly that. If you've ever wondered how it would be if everyone knew that Nanoha is a magical girl look no further also - Galaxy Fraulein Yuna is set in a world where everyone knows that Yuna is a magical girl. 

They both have giant fighting mecha ^.^ however, Galaxy Fraulein Yuna is more aimed at girls I think. But, if you like fighting mecha then you'll probably like both of these ^^