Mai/Tate have my blessings, because it's fun watching their cats-n-dogs relationship. I like it
(I do however think that Tate needs a kick in his rear end. The way he's been treating Shiho over the last episodes wasn't remotely acceptable)
And "the single main plot"? You gotta be kidding
... there's so much going on at the same time. No, unless I'm off with my dark predictions, I suspect that the theme of the second half will be something between "survivor" and "last girl standing".