Chapter 6 Stage 2 was my choice for grinding. If you've done everything but still haven't hit 72, there is a way to quickly grind up. You hit Taki with that and you'll take off nearly all her health with it. You'll see a blue flame around Nightmare's weapon if you're doing it right. Try it in Practice and you'll get the hang of it. Use AAB (X, X, Y), but leave a pause before you press Y. But, there is a move Nightmare has which for some reason will nearly take her out in one hit. The rest go down to your 66B shenanigans like anyone else, but Taki doesn't. The problem? You don't have a lot of time, and Taki is pure evil. You face Mitsurugi, Voldo, Taki, Nightmare and Cervantes. This is the one you need to play when you reach Level 72 to unlock Subchapter 2 (and by extension, Lizardman). The stage that gave me the most trouble was Chapter 4 Stage 3, Merope Monastery. The rounds where you need a ring-out also caused me some trouble, but using Nightmare's 4B (back and Y) seemed to get the job done, I also switched to Xianghua and spammed her 4K (back and B). In the rounds where you need to hit the opponent a certain amount of times, Nightmare's a bit too slow, so switch to someone faster (I went for Sophitia). There are some fights where it doesn't work so well though. And finally, forget Soul Edge (Complete) and take up Soul Calibur when you have that available. In terms of weapons, switch to Flamberge (damages through guard), but switch to Soul Edge (Growth) when you can. It's not a perfect method though, there will be times the AI will kick you down, but this method is the quickest/easiest way I found. It's also a fantastic way of getting the '10 Perfect Victories' achievement. For some reason, the AI just sucks against this move, and it will win you a good 90% of your fights. Keep using his 66B attack (dash/double-tap forward and Y). To make Weapon Master a cakewalk, use Nightmare.

If I realised it earlier, I could have saved myself an hour or two. I got it in a day, and that's with using a variety of characters for most of it. In theory this isn't too difficult, or that time consuming.

Edge master soulcalibur