Given that Yuu's (or rather, Strength's) attempt to enter Black Rock Shooter's world to save Mato has failed, is there any way of returning things to normality?
As far as Strength is concerned, there's only one thing for it - to end her life and thus toss Yuu (aka Black Gold Saw) back into reality, which unsurprisingly Yuu herself is none too keen on. Neither, for that matter, is Mato, and it's her reaction which turns this world decidely topsy-turvy. Before we know it, Black Rock Shooter is facing off against herself in the form of Mato, with the latter individual's insistence that she's ready to take on any pain required to protect others being taken rather too seriously by Black Rock Shooter, who proceeds to knock the living daylights out of the poor girl.
Thus, much of this episode is effectively Mato's brutally violent fight against her alter ego, with the other characters whose lives Mato has touched regaining their memories of why she's so important to them enough to cheer on from the sidelines. Ultimately, Mato defeats Black Rock Shooter and causes the world she resides in to explode with colour, meaning that the day is won and both Mato and Yuu can return to normality, even if Black Rock Shooter's world continues onwards as ever. The moral of this story? If you have a split personality, destroy it with a massive energy weapon.
If I had to sum up Black Rock Shooter in a word, that word would be "huh?!" - very little of its core concept felt particularly coherent, with overblown melodrama offset by stylish but largely pointless action in a world where none of the characters can die as a result of said action. It's this horrible shoe-horning of drama and action that destroys any credibility Black Rock Shooter deigned to have, making it feel like the clumsy attempt to sandwich a popular character into an anime series that it clearly is. Given how great the action component of the show frequently looked (some flaky CG aside), it feels like an utter waste of that particular art style and presentation, and I can't help but think the writers could have found a better way of introducing that world without all the overblown nonsense it relied upon here. In comparison, even the Black Rock Shooter OVA felt a little more coherent, and that's really saying something.