Both are mid-90s series about a group of girls (presumably sisters) who pioneer their way through new fields in society to reach the top and achieve their dreams. Cute side characters are sprinkled throughout along with a decent dose of silly and serious moments. Catchy J-pop songs, group dynamics about how to work as a team, discovering hidden secrets about the dark side of their work, and the influence of an outsider are prominent features in both series. They also have similar animation styles and character designs.
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.
Bubblegum Crisis inspired many series and Metal Fighter Miku is most likely one of them.
Four main female characters - check
Metal/Mecha suits - check
Fighting sequences - check
Cool soundtrack - check
Be advised that Metal Fighter Miku is not as great as Bubblegum Crisis, but nonetheless it's still a really good series.
Futuristic, unusual competitive sport and main character growing into the role is what these two anime have in common.
In Metal Fighter Miku it's Neo Pro-Wrestling - a version of pro-wrestling where fighters (all female) use metal suits.
In Battle Athletess Daiundoukai it's a mix of futuristic versions of some well known sports (e.g. zero-G lacrosse).
Our main heroine vows to beat the strongest wrestler in the world. One series takes place in the future while other does not. Sakura is an idol singer while Miku is a normal girl who loves wrestling. Sekai de Ichiban Tsuyoku Naritai has fan service + idols + wrestling while Metal Fighter Miku has no fan service. Both series depict the art of wrestling.