It foiled 3 different online handwriting input websites. I tried looking it up via radicals to no avail. The rest of the characters in this font were quite easy to get.
I had decided on "ざ"
Thanks for adding the context. It is indeed ぞ. The whole thing is:
EDIT: Looking for more context I tried to google it and it seems the title of some kind of erotic anime or manga? That was kinda embarrassing since I'm at work and a quite inappropriate picture came out. Lol :)
It would be must easier if you gave more context but off of just this I would just guess ぞ (zo).