Episodes of Oreimo are like buses... they often turn out to be full of creepy people in the end.
Anyhow, before this triumvirate of finale episodes to the series, it was clear that Kyousuke had finally made a decision as to where his heart lies, and having brushed off Ayase his next job is to make it abundantly clear to Ruri that he's now in love with someone else... namely Kirino. In spite of her knowing this the whole time, Kuroneko is still understandably torn up by the whole thing, but apparently not enough to play at least some role in Kyousuke's next plan - to invite Kirino out on a Christmas date under the premise of getting some exclusive merchandise at a couples event at Akihabara, although what he really wants to do is confess to her. After needing to give chase after Kirino gets the wrong end of the stick initially, things don't look much better when she gets the right end of the stick, calling Kyousuke creepy and an awful lot. Until he asks her to marry him. Then she says yes. "What?!" I hear you cry. Yes, quite.
So, with this pairing now finally admitting their feelings for one another, what next? It's time to play some eroge of course! Alongside that, it's also time for Kyousuke and Kirino to decide their future, and the next thing we know this "couple" are dating, albeit in that kind of oh-so innocent way that only happens in Amish populations and anime series. This means that Kyousuke also has to wander out rejecting the advances of any other girls who might otherwise leap upon him, namely Kanako who chooses to confess during a live event yet somehow manages to (I assume) escape without being burned alive and strung up by her rabid otaku following.
With support from their friends and the like, things seem to be going pretty well for the couple in spite of the obvious difficulties of their situation - this is, however, a scenario that childhood friend Manami simply won't put up with. Well, I say childhood friend Manami, but she's actually played in the show's final episode by Kamijou Touma from A Certain Magical Index (she even heals as quickly as he does), causing a punch-up between herself and Kirino. Even here Kyousuke refuses to back down in his love for Kirino, leaving yet another girl crying in his wake because he's fucking insane. With all obstacles now removed, we eventually discover the truth behind Kyousuke and Kirino's relationship - this was simply a limited-time offer until their respective graduations, after which they return to being normal brother and sister. Considering they didn't actually do anything before this point, couldn't they have just gone back to being normal siblings at the start of all this nonsense and actually allowed Kyousuke to have a normal high school life?
Ultimately, such questions are all but pointless in the face of three episodes which showcase the absolute best and worst of the series - getting to see Kirino and Kuroneko argue about anime one final time was just one reminder of what this show could do really well, but on the other hand watching Manami's character change entirely in this second season was equally a reminder of how these later episodes felt more like some kind of particularly screwball fan fiction that somehow got mistaken for the show's actual scripts. If you can buy into the whole "incest for the win" concept (yes, that is an actual line in the final episode), then these final three episodes aren't entirely terrible, but even then they've managed to completely negate what made this series successful initially, turning a comedy about otaku with some romantic undertones into an absurdist harem comedy that only kept mentioning eroge in a desperate attempt to hold onto its roots. This second season of Oreimo hasn't entirely destroyed all of the good work of the first, but by the end of it all my enthusiasm for the franchise as a whole has largely been reduced to a smouldering wreck, like so many light novels burned by Kuroneko fans.