Not much to say here, besides that the final battle begins in episode eleven of SENRAN KAGURA SHINOVI MASTER.

The door to the other world has been opened
This episode begins with youma pouring into the human world from the other world, after the door between the two has been opened. With all the jounin busy elsewhere, it falls to the shinobi students to tackle the youma crisis.

Miyabi outright kills the youma instead of weakening them to be sealed
The plan for fighting the youma is to weaken them enough so that Asuka can seal them afterwards. However, Miyabi has no intention of going along with that; as far as she is concerned, it is a shinobi’s job to defeat youma.

Katsuragi has a plan for gathering the youma in one place
As things stand, the youma are scattered around and thus difficult to seal all at once. Katsuragi has an idea for solving that conundrum, which requires the help of Ikaruga, Shiki, Mirai and Ryona. Actually, they get very little say in the plan, in which they are bait for the youma.
Katsuragi’s plan actually works, and Asuka seals a large group of the youma. However, she is unable to hide the side effects of using Fuma Korin any longer. Fubuki and Rasetsu arrive moments later, and Fubuki tells Rasetsu to crush Asuka’s hands.

Homura & Miyabi prepare to fight Rasetsu
Reinforcements arrive before Asuka can be seriously injured. Homura and Miyabi confront Rasetsu, whilst Yumi faces Fubuki.

The final moments of Fubuki’s parents
A flashback scene shows how Fubuki had to watch as her human father had to seal her youma mother. Using the Fuma Korin technique brought Fubuki’s father’s life to an end, so Fubuki had to endure losing both parents in that one moment. Rasetsu fled with her afterwards, eventually asking Kurokage to take her in.

Fubuki vs Yumi
The fight between Fubuki and Yumi is interspersed with memories of the time the pair spent training with Kurokage. It comes down to the pair of them attacking with all that they can muster, but the outcome of the fight is not revealed here. This is where this episodes ends, after all.
Oh, hey, look. Another episode where Yumi steals the spotlight. The preview for the next episode suggests that Yumi is dead, but I don’t buy it for a moment. The studio probably doesn’t even have the guts to kill off Japan’s favourite Senran Kagura character. Go on, TNK, I dare you to prove me wrong.
Fubuki’s tragic backstory has been revealed, and I didn’t really find myself invested in it. It isn’t anything particularly new.
Whilst I’m sure that Yumi won’t be killed off, her being out of the picture for now will give some time for the Asuka, Homura and Miyabi to shine. Well, at least I hope that is the case. Ideally they’ll get some pretty neat fight scenes before Yumi inevitably returns.
This episode was all right, I guess. Katsuragi’s plan was a highlight, and I’m in total agreement with Miyabi when it comes to slaying youma. Some may be almost human such as Rasetsu, but that didn’t really seem to be the case with the youma that the shinobi were fighting here.
The problem with sealing away evil is that seals tend to break.