I can't remember if I mentioned this before, but since I recently finished a 2nd play through of Tengai Makyou Zero as part of the beta testing, I would love to see someone take care of some serious balance issues in the game (don't worry, no spoilers follow except as they relate to game systems):
--The scroll system for magic and the way characters gain battle skills is great and really encourages explroation throughout the game, but the usefulness of these things vary wildly. For example, status effect magic is almost uniformly worthless for the heroes (although very useful for enemies), making it ridiculous when I get late-game status effect scrolls I'm almost guaranteed never to use. Buffs/debuffs should also be rebalanced as with the exception of Sting, most of them don't do much.
--Also, certain characters bring scrolls into your party, and a certain character that brings a lot of attack magic really breaks the game balance as those scrolls are pretty powerful for the point at which they join. This is another beef--there are 2 tiers for attack magic, but the power jump is pretty massive, although by the end all the attack magic is mostly worthless. Rebalancing these while fixing the utility of ~50% of the scrolls would be very welcome.
--Item access problems utterly break the game starting about halfway through. It is very possible to get a setup that maxes out the defense values of your hero's equipment at this point, and there are certain items you can purchase for relatively paltry sums that make magic restoration items almost completely unneeded after this point. Doing something about this would likely fix most issues with difficulty by the end.
--Similarly, the first 3 godstones are absurdly more useful than 2 of the last 3, and while I believe their powers are meant to stick with their respective god's theme in japanese folklore, they should really be rebalanced a bit to be more evenly useful rather than frontloaded.
--Generally just rebalance enemy movesets to make better use of status ailments. They're used pretty sparsely for ~3/4 of the game, but then show up out of the woodwork later, normally by the time you've got all the right equipment to make them wasted turns anyways. Again, item access could help here, but I think better use of ailments early on would be a good idea, among other AI improvements.