Harder + Faster = Better :)

I　agree with Truncated, less shurikens simply makes the run look slightly more choppy in the beginning before you get at least 100 shurikens in the second stage. There is no point to a 0 shurikens run IMO. Truncated: Expert difficulty only does two things: A smaller life bar (only has 8 bars instead of 16), and you get less lives (2 IIRC). Both of these factors do not make any difference in a speedrun/TAS because you don't want to get hit and I don't think mijin is useful in more than 2-3 places. If you wanted to save a little time you don't have to pick expert mode.

So there's not more enemies, harder enemies/bosses, perhaps with more health?

I'm not sure. But if there's a difference in number of lives as you say, I think playing in hard is a better idea. So, you get 2 lives, plus one extra in the second level which you can get without wasting time. The only given jutsu is mijin on stage 2 boss. The other two mijin is either on stage 1 boss or stage 3 boss. I need to test where it saves the most time compared to just whacking them over the head. Other options: mijin+fire and mijin+fire, or mijin+mijin and fire+shuriken. Stage 4 (water and pipes): perhaps fushin if there is some part where it's useful to skip parts of the pipe section. Otherwise I don't know. Stage 5 (electric demon): Can't think of anything here. Maybe fushin for the vertical climbing but probably not. Mijin and kariu has no effect on the dynamite, right? Stage 6 (traps): Fushin for the vertical trap rooms. There's a free jutsu point here but I'm not sure if it's useful anywhere. Stage 7 (final level): Ikazuchi for the electric floors. There's another free jutsu point, maybe use fushin for the final vertical climbing section, but I'm not sure if the jutsu animation makes it worth it. All in all I guess I need to do a lot of testing before I can get anywhere with this. I know who to ask when I have questions, at least. :) Any closer to making a new speedrun attempt at this game, by the way?