A newgame+ run of WEWY would be dramatically different from a fresh game. The game unlocks more and more features as it progresses (and there's many), which would all be saved in a newgame+. A newgame+ from Shiki, Day 1 would then have everything already unlocked, not to mention you keep your level, equipment, and attributes from before.
I highly doubt you would be allowed to use AR or whatever to unlock just ultimate mode, unless there's some unknown in-game code to unlock it.
My suggestion if you want to TAS this game is that:
You have to start from a clean SRAM.
Everytime you level up, you revert the LVG back to 1
You use the highest difficulty as it becomes available
Make it entertaining.
http://twewy.wikia.com/wiki/
If you haven't already stumbled across it, I'm sure this page will help you out.