Originally Posted by Nefelpitou

Jigen Tou:
I have also been doing some reading on the Jigen Tou. It is a very wierd power. It contains some similarities to Super Buu's and SSJ3 Gotenks' Kiai. Like the Kiai, the Jigen Tou could cut dimensions. The Jigen Tou was even capable of making tunnels between dimensions in the final volume of the manga. It is much like Itsuki's power to make little temporary tears in dimensions that allow small groups of people through. That is where the similarities end in the manga end. Kuwabara's Jigen Tou was also capable of not only merely making tears in dimensions, but causing tears so traumatic to dimensions that it causes the dimension to distabilise and just collapse. This is similar to the DBZ anime filler version of the Kiai, as Super Buuhan almost caused the collapse of dimensions with a sustained "Super Kiai".

But the BIG difference between the Jigen Tou and the Dimensional Kiai is the Jigen Tou's sheer unstoppability. There was nothing in the entire Yuu Yuu Hakusho manga that could stop the Jigen Tou. It could slice through people regardless of their power level. It could cut people as weak as Mitarai and it could possibly even slice through people as strong as Sensui. Sensui always dodged the Jigen Tou when he could have just taken it like he did with Hiei. This provides the most likely explanation as to why Kuwabara's blade could destroy the Kekkai: it could cut through anything. Super Buu's Dimensional Kiai could cause dimensional rips due to the sheer power of his Ki. If it was like Kuwabara's Jigen Tou, Super Buu's Ki would have killed everyone it touched. However, we see DBZ characters taking hits from Super Buu's strongest Ki attacks and surviving.

This shows that Super Buu's Dimensional Kiai is very different in nature to the Jigen Tou and cannot be compared, as it does not contain nearly as much cutting ability as Kuwabara's Jigen Tou. In fact, if we cannot accept anime-only evidence here at MFG, then Super Buu's Dimensional Kiai is more similar to Itsuki's dimensional ripping in the effect it causes. A temporary tunnel to other dimensions. The Kekkai could only be affected by either Reikai's spell-casters who put the thing up 50 years ago (as Raizen said there was no Kekkai 700 years ago) or by something that could cut through anything. Sensui deemed that if he found a "cutting power" that could "rip entire dimensions apart" (Viz Vol. 14), something Itsuki's dimension ripping power couldn't do, that should be close enough to the power to cut through anything. Mitarai thought Kuwabara might be the one when he saw the cuts in dimensions, but only after he saw his entire dimension collapse did he say that Kuwabara was the one.

Natural dimensional distortions:
My final input into this thread is that if the reason for the natural, sporadic dimensional tunnels between Ningenkai and Makai was due to the dimensions being weaker than those in DBZ, then there would have been sporadic dimensional tunnels from those realms to other realms as well. There were no natural tunnels to Reikai, but such tunnels were shown to be opened in seconds, whereas tunnels to Makai of a similar size took hours. This information suggests that the natural dimensional distortions weren't due to the "weakness" of the realms. What it does show is that the reason why it happens is more complex that just that.

In fact, the reason given for these sporadic openings in the final volume of Yuu Yuu Haksuho is that they were essentially God's Will. In the same chapter Kuwabara used his Jigen Tou to open up a portal to Reikai, we learn of the omnipotent, omniscient, etc. God of Yuu Yuu Haksuho, who created everything according to His Divine Will. However, we learn at the end of the chapter that God also controls every little thing in the Yuu Yuu Hakusho world with his Divine Will. Every event in YYH, every battle that was ever fought was started, fought and finished due to God's Divine Will. God's Will was also given as the explanation for any random, sporadic event, such as the openings between Makai and Ningenkai. It also explains why there weren't openings from Makai/Ningenkai to other worlds despite the fact it was so easy to open portals from Reikai to Ningenkai, but so much harder to open portals from Ningenkai to Makai.