如何在PHP中从IMAP检索Unicode字符？

I'm trying to parse an email that is partially written in English and partially written in Japanese using PHP. Here's the code I have so far:

if ($mbox = imap_open($mailbox, $username, $password)) {

    $inbox = imap_check($mbox);
    $total = (int) $inbox->Nmsgs;
    $min = max(1, $total - 10);

    // fetch 10 most recent emails
    if ($total > 0 && ($emails = imap_fetch_overview($mbox, "{$min}:{$total}"))) {

        foreach ($emails as $email) {

            $body = imap_body($mbox, $email->uid, FT_UID);

            // for testing purposes
            echo $body;

            // parsing logic here

        }
    }
}

So as you can see I'm just echoing out the plaintext body of the email, just to test things, and here's part of the echoed response I get when I run this script:

Your Japanese word of the day is: ç”·ã®å­

However, the following is what I should see in place of that, based on what's actually in the email:

Your Japanese word of the day is: 男の子

So clearly something's being lost in translation (pun intended). I'm using some simple string manipulation to try and parse the Japanese characters, and then insert them into a MySQL database. However, it's currently inserting those gobbledygook characters instead. What am I missing?

Edit: I'm using PHP version 5.4.45

So I'm not really sure how to get this working in PHP 5. I decided to try upgrading my server to PHP 7 and suddenly all of the code just started working.