1 Is it a really strange version of そ?

2 Correct.  It's a classic hand-written version of "so".

3 It's a bit more noticeable when you see the "ten-ten" mark when it shows up for "zo".
In other news, I feel great sympathy for left-handed Japanese.  Stroke Order is extremely important in handwritten Japanese not because it's the "Japanese being Japanese", but due to being nearly unreadable if you don't follow the proper order.  Context and "slant" are how a lot of it ends up being read, realistically.  So it's really rough when you write with the opposite hand.

4 I'm late to the 'そ' party but I'm going to mention that I was sure the question was about the character... er. the girl in the picture.

5 Her name is Miura. She's the one who defeats Vivio in the tournament.

6 In case anyone's interested, this is from chapter 66 of the Nanoha Vivid manga, which hasn't been translated into English yet. (The translation project kind of stopped. The last chapter was 54.)

7 Where do you get the raw scans?

8

There have been torrents. I just downloaded this one, for instance, which had the first ten collections.

The chapters that have been translated I've gotten from other web sites, in particular this one and this one.

The last raw chapter I have is 72. The last translated one is 54.

Which is frustrating. There's something really important that happens in chapters 58-61 (in Volume 12), which results in Vivio beating the crap out of Einhart, and Einhart smiling for the first time afterwards and I can't figure out what brought it about. From other things I've read elsewhere, Vivio has found her "Sankt Kaiser" mode, which is what she used in StrikerS when she fought Nanoha in the guts of the Cradle. It's profoundly more powerful than her normal "Adult" mode and that's what she uses to beat Einhart. Visually, the difference is that her jacket in "Adult" mode is white and in "Sankt Kaiser" mode it's dark.

I am probably the world's worst Japanese-to-English translator, but I've been trying to pick out particular word balloons which I hope might shed light on the situation and then translating them in my own slow, pitiful way.

But I haven't gotten any hints. Another mystery is that after Vivio won, Nove chewed her out royally for some reason.

9

The biggest reason I want to know what happened in 58-61 is that it's a life-changing experience for Einhart.

[/spoiler