Try this instead:
Regexp reChar = regexp "[\\\\]u([0-9]+) +\\?"
Or even better :
Regexp reChar = regexp "\\\\u([0-9]+) +\\?"
If you wanted to search for the brackets and not for the backslash, use :
{code}Regexp reChar = regexp "\\[\\]u([0-9]+) +\\?"{code} regexp "\\[\\]u([0-9]+) +\