Great app, but room for improvement

I love this app. Its great for drilling sound-symbol relationships, but there are a few simple improvements Id like to see .

1. It would be useful to be able to select (or deselect) individual characters rather than just series. Sometimes I want to target a half-dozen symbols (in different series) with which Im experiencing difficulty, and thats impossible to do. It could be done without complicating the UI (the simplicity of which I love) by something like having a series become grayed out when its selected, and then touching individual symbols to deselect them, or the other way around.

2. In order to be able to work with new symbols (or series) more intensively while still being exposed to ones Ive already learned, I wish that there were a way to designate the frequency with which particular characters appear. Even something as simple as being able to select high, medium, or low frequency would be helpful in terms of user customization. Could be done without complicating the UI by combining the idea about graying out selected series with using a light, medium, and dark shade of gray.

Po-san about Real Kana