In POT, the yips is not something Yukimura himself has control over. He says stuff like: "It appears you lost your sense of touch." If he was the one activating it why would he say a thing like that? It'd just be "I took away your sense of touch."
At any rate the whole notion of yips as some effect from intimidation is pretty bogus, because Fuwa was not at all intimidated by Yukimura. With Hyakuren + Saiki Ryoma was firmly in control of the fight to the point he can predict when he'll win, so why would he suddenly get scared by Yukimura who obviously can no longer return everything he's hitting?
By NPOT it seems like Yukimura have more control but in POT he does not, not that it matters since he can return anything so it's really irrelevent when yips kick in. Yips, at least in POT, is something that sort of just happens when you play Yukimura for no apparent reason. It doesn't matter if you were winning or losing, if Yukimura says you got yips, you got yips. The only reason he's not unbeatable in NPOT is that he lost his 'whatever I say is right because I am the final boss' status. That is, we wouldn't be surprised to see a guy like Tokugawa saying, "LOL yips is nothing" because Tokugawa is easily a higher tier character than Yukimura. He wouldn't even need to justify why yips is nothing. It'd simply be nothing because he said so.
But Yukimura enjoys the "I am right because I said so" advantage over every character in the middle schooler level aside from TnK enabled characters, so he won't possibly lose to any of them, at least as of POT.
---------- Post added at 08:43 PM ---------- Previous post was at 08:34 PM ----------
For Saiki versus Hyakuren, Saiki might help on borderline returnable power shots, but it'll do nothing against obviously unreturnable power shots. Let's say you're Tezuka without TnK and you're up against Duke and he hits a Duke Homerun. If you only use Saiki by itself the only possible solution is 'whoa this is going to hurt'. You can't possibly return that. With Hyakuren you can at least attempt to return it. It's unclear if Hyakuren works on power techs THAT strong, but at least you can try.
For In versus World of Ice, World of Ice is a physical observation, as in 'due to my enhanced eyesight I can see that you standing in this position you cannot possibly get to this, that, and that spot on time." It is not about reading what your opponent plans to. The icicles represents a physical blind spot that is an inherent physical property of the game. Rai's speed wouldn't help becase again the blind spot is somewhere you can't even see so even if you can teleport you still wouldn't know the ball's being hit there at all because you can't even see it. You can argue if you're at Sanada's level who has only one icicle (that's what World of Ice reveals against Zan) maybe if you knew where your own weak spot is then you can teleport there and hit it even though you can't physically see it, but that sort of implies you got World of Ice too to see your own weak spot.
Intuitively you could just start way back by the back wall, and since you're so far back all your blind spots must be outside of the court so Atobe cannot possibly hit to them without losing a point, so he'd be forced to hit somewhere inside the court and you use Rai speed to get back in the court after you see the shot is being hit. That said you'd have to use Rai twice to return World of Ice (first time to get way outside of the court, second time to get back inside the court) so that could get pretty nasty in terms of tradeoffs.
---------- Post added at 08:47 PM ---------- Previous post was at 08:43 PM ----------
Oh, and for Eiji's interview in Pair Puri, doesn't Yukimura use Yips to take away Eiji's taste? But I'm not too sure how seriously you should take that, as it is just a joke.
He can flat out take away all 5 senses so I don't see why taste is anything more special than anything else. He probably doesn't do it while playing in tennis because that's not a particular relevent sense.
I can just see Yukimura try to take away Fuji's sense of taste and Fuji will be like: "Sorry, but I don't have a sense of taste."