I realise that this is probably a known thing but my google-fu is not
working today.

I am learning Japanese and I wanted to write an application (probably
a web app) that I can paste some Japanese into and highlight the
characters that I should know. To do this I need to take a string of
Japanese, such as "目が覚めてしまった。眠いのに…。" and break it down into
characters, that is this string contains 16 characters and a space
(despite being 49 bytes long).

Of course some strings also contain latin characters mixed in, such as
"俺の嫁と会話2 | あねこ".

My home-brew solutions always seem to screw up, but then I thought.
This is Ruby! Why the heck am I reinventing the wheel?

So can someone clue me in on how to take a string of Japanese and
break it up into characters?

Please