There's no way around Tate-Mai. Sorry, that would totally shock me if THIS was going to happen. They have all indications of modern anime relationship theory going for her
Shizuru is as gay as it gets. Just look at her harem fighting over putting sunscreen on onee-sama. I hope that she'll continue to work on Natsuki ^_^ ... that would be just a WONDERFUL pairing continuing Natsuki's affinity for deeply embarrassing moments. Besides, Shizuru is clearly the girl Natsuki is closest to, and cooperating with the most.
Kendo guy has been reduced to a humorous sidekick in ep13. No chance for Natsuki, sorry.
Kanzaki - no matter what he was telling Mikoto earlier on, I still think he's ani-ue, or at least somehow linked to him.
And of course Yukino is _definitely_ romantically invoved with Haruka. This one will also be interesting to watch.