use JSON 'decode_json';
use Data::Dumper;

my $mangled_json = '{ "hex_code":"\\x{a5}" }';
print $mangled_json;
my $json = $mangled_json;
$json =~ s!\\\\!\\!g;
print $json;

my $structure = decode_json( $json );
$Data::Dumper::Useqq = 1;
print Dumper $structure;

binmode STDOUT, ':encoding(UTF-8)'; # well, hopefully, your terminal understands UTF-8
print $structure->{'hex_code'};