how to unlock i phone 6 purchased from japan

As far as I know, Japanese carriers do not unlock iPhones. You can try contacting the carrier to which it is locked and asking them.

The JV SIM is a hack and possibly illegal. Japanese carriers do not unlock iPhones. ONLY the carrier it's locked to can legally authorize unlocking it. Apple won't do anything for you. Buy a phone you can use.

Yes, it is. Purchasing a phone in a country you do not intend to use it in is never a good idea. The iPhone warranty is not international, and is only valid in the country of purchase. This means you would have to take the device to the country of purchase for any service. In your case, back to Japan. Simple research would have revealed that Japanese carriers do not unlock phones. Purchase a phone locally.

No. ONLY the carrier it's locked to can authorize unlocking it and the Japanese carriers will NOT do so.

If there was an option, none of us would have been telling you that you couldn't get it unlocked. As you have been already told, only the carrier can authorize the unlock of the device. Japanese carriers do not unlock phones. In addition to that, you were willing to hack the device, void the warranty and risk bricking the device. You were further advised of the problems with purchasing phones from a country you do not intend to use them in, and without understanding what carriers in that country will do. Like I told you earlier, purchase a phone in your home country.

You're welcome.