Preview your page in the SDL Tridion CME and check if the expected Japanese characters are showing up - I am pretty sure, you will be able to see the correct Japanese characters unless you have done some explicit wrong coding in the template related to the Character Encoding.
If the Above stands true, go to the (or may be ask your system admin) to check for the Publication Target (on which you are publishing) and ensure the "Default Code Page" is set to at least UTF - 8 (and not the System Default), see the screen shot below:
If it still does not resolve the issue or the above two things are set up as expected, then go the web application server and see if the encoding for the website has been set up correctly.
For example: If your end application is ASP.NET based, in the corresponding web.config, you may need to add the below line:
<globalization fileEncoding="utf-8" requestEncoding="utf-8" responseEncoding="utf-8"
I hope it helps