Effective as of 1st September 2019, AU phones can now also be SIM-unlocked under the new less restrictive policy. If you have a contract phone, you can remove the SIM lock after 100 days have elapsed since purchase, or if you have paid your device in full.
If you are a contracted subscriber, that is, you bought your phone directly from AU, you can remove the SIM lock yourself, from your MyAU account, for free.
The situation with second-hand phones, however, is the same as with SoftBank: to unlock a device you've bought from another user or from a used-phones shop, you need to take it to an AU store and pay the 3000 Yen (ex-tax) fee.
Further conditions include that the device cannot be unlocked if it has been restricted from network usage, or if it is damaged or wet (the unlock will only be performed after the phone is repaired).
You are only allowed to SIM unlock up to two devices per day.