Ok, I have no idea how to tag this. This is a character named Emily, from what I think is a fanmade RPG (or just a video simulating an rpg?) named Chikyuu Boutai no Kessen, made by Takahashi Kuniko.

The video can be found here: http://www.nicovideo.jp/watch/sm6101989

I can't load niconico but tagging that is easy from what you say in your post. copy:Chikyuu_Boutai_no_Kessen char:emily

Or at least that's how I'd do it. It doesn't matter if the product is a doujinsoft or not. Look at the massive touhou tag. That's a doujinsoft series.

I figured it out, actually. Some guy has been posting gameplay videos of little RPGs that his sister made (妹が作った痛いRPG). They're really weird, though more like flash games than RPGs. This particular one starts out with a guy killing a God with Jesus Flash...

I will create tags for it, though I doubt they'll ever get used again.