First more then likely you'll have to beat NG and NG+ for this but it is worth it

First time you beat the game make sure you do the good ending meaning don't kill the maiden in black just leave the old one

Next after the credits you should get The Maiden in Black Soul -important-

After going through the game save Biorr and then from the official get the bloody Key Ring

After you have the key go save Yuria the witch see teaches you the Magic Soul Sucker

After you've done that beat the game again in NG+ by this time attacking the witch and becoming a demon for the old one

You at the point after the credits should recieve the beast soul worth 200k and the (Red Eye Stone)- Challenges a player instead of invade works like blue eye stone but your a black phantom

Now all you have to do is equip Soul Sucker and have someone you trust Soul *** you or the other only 1 person can go at a time

After that person finishes

-IMPORTANT- The person who got soul sucked must quit the game or turn off ps3 that way the lvl doesnt change (sometimes you may lose a lvl but in long run easiest way to lvl.

Also remember there is no thing as a legit lvl 712

P.S. feel free to add me on the PSN user is the same here Blitzmafia for those who dont want to scroll up