Takahashi Itsumi's Love Flag Girls!! is, truly, trashy romance manga at its goofiest. For something silly and smutty, this series is a fun pick. ^_^
Queen Beatrice spends all of her time crying over the cross that the dreaded pirate Maria stole from her years ago. This cross is apparently valuable enough to buy a small country. Upon learning that Maria's ship is right in the harbor, within walking distance of Beatrice's castle, Beatrice's daughter Princess Lucia decides to infiltrate Maria's crew and get her mother's cross back.
Turns out Maria disappeared without telling anyone where she was headed, and her ship is now being captained by her daughter Eliana. Contrary to what she'd always been told about pirates, Lucia finds that Eliana's (all-female, very gay) crew is quite welcoming and laid-back (aside from Eliana's rather serious first mate Isabella, who is in love with Maria), and Eliana herself is a goofy flirt.
You'll be shocked to know that Lucia reciprocates Eliana's attraction, and she and Eliana fall in love. As I mentioned before- because this is not only a Yuri Hime series, but a YH series that was serialized as a cellphone comic instead of in Yuri Hime magazine- there's some pretty explicit sex.
Just as Lucia starts getting acclimated to pirate life, Beatrice sends out the navy to attack Eliana's ship. Lucia returns to the palace to reason with Beatrice, but Beatrice sees it as a betrayal and has her jailed.
Eliana saves Lucia and slaps Beatrice, telling her off for letting her obsession with the cross warp her view as much as it has. But Beatrice's real obsession isn't with the cross- it's with Maria. Maria and Beatrice were a couple once, but Maria left Beatrice because, as a princess and a pirate, how could they be together?
Lucia and Eliana escape back to Eliana's ship, but Beatrice's troops quickly corner them again.
Won't spoil how (although it shouldn't really be surprising), but we get a happy ending. =)
I enjoyed the heck out of this series, but I don't want to make you think it's more sweeping and epic than it is. It's a humorous, anachronistic, alternate world take on the historical pirate adventure genre with lots and lots of yuri. ^_^ Even the battles aren't taken that seriously- mostly thanks to Eliana. Eliana and Lucia's involvement with each other is initially contrived (and, briefly- to the point that I admittedly forgot it until someone else mentioned it- has some questionable consent interaction early on), but they grew on me and I came to like them as a couple (e.g. their argument about which one of them is cuter) and found it easy to root for them. (Not that there was ever a question that this story would end happily.) I also enjoy the fact that, even living in a late 17th century Spain (best as I can tell)-influenced setting, the characters live in a world where being in a gay relationship isn't an issue at all- and like that, however cheerfully stupid it is, LFG has a setting and plot that's different from most yuri.
In short, recommended if you're looking for a frothy, bawdy, smile-inducing yuri romance.
Story: Fun trash.
Speaking of yuri manga, for anyone who hasn't seen it, here's a fake pulp magazine cover Erica from Okazu made that I thought was funny/painfully true.
And if you want a good lesbian romance novel with a pirate adventure theme, I recommend The Sublime and Spirited Voyage of Original Sin by Colette Moody. It's about a pirate captain's daughter and the seamstress who sticks with her after helping tend to her wounded crew after an attack on her ship. It isn't as light as Love Flag Girls!!, but it's a lot of fun also.