how to unlock iphone 5s kddi au

It is becoming possible to unlock smartphones with Japanese carriers since the government changed the rules in late 2014: http://www.reuters.com/article/2014/10/31/us-japan-mobilephone-simcards-idUSKBN0 IK0EU20141031

I'm looking to do it with my AU KDDI iPhone soon. Any info would be greatly appreciated.

You contact the carrier it's locked to and find out what their policy on unlocking is and whether you qualify.

According to this: Wireless carrier support and features for iPhone in Asia-Pacific - Apple Support The Japanese carriers do not offer unlocking.

You still need to contact the carrier to get it unlocked.