For those of you who are keeping up with Yozakura Quartet: Hana no Uta (and if you're not, you should start...what's wrong with you?) you may have noticed a slight...hiccup in the story.
All of a sudden there's a new character and not a lot of backstory to go with her. It's a little jarring, to say the least.
Rest assured, this is only about 3/8 bullshit.
As it turns out, the team that does YZQ: HU put together 3 OVAs in 2010 called Yozakura Quartet: Hoshi no Umi (coincidentally, ALSO YZQ: HU). These OVAs cover all of the missing information and serve as the unofficial episodes 9, 10, and 11 (or 8.25, 8.5, and 8.75 if you prefer).
In fact, they fit so perfectly into the hole in the plot, that I'm even willing to subscribe to the theory that the creators of Hana no Uta were saying to each other "Hey, do you remember those OVAs we did that were so popular? Why don't we just work that into the show. It'll save us from having to do that whole arc again."
To be completely honest, I don't think any amount of exposition or flashback sequences can do Hoshi no Umi justice. So...just do yourselves a favor and watch it, there's no reason not to.