[deathanatos]

The original prompt is a bit under-specified. (But hey, that certainly matches the real world!)

You're going to have to buffer at least a little, to figure out where the USV / grapheme boundary is, depending on our definition of "character". To me, a BufReader is appropriate here; it avoids lots of tiny reads to the kernel, which is probably the right behavior in a real case.

To me, "read character by character" vaguely implies something that's going to yield a stream of characters. (Again, for some definition there.)