"Convenient"? No, it's only logical. They are the last defense for the Spirit King, after all. They should be expected to be ridiculously OP. And I don't know if you noticed, there was only one pillar, and it just arrived :/
I liked Mayuri's explanation. Kon's part was completely random and pretty stupid, imo. As for Squad Zero, they look pretty interesting. It was a 3/5.
Oh come on, you know how it works. This is just the classical gap in a story where the hero is on his knees thinking about what went wrong, they were all so happy before.
Now there will be a training montage, Ichigo/Ikkaku/Renji running up some steps with one of the squad Zero's holding a stopwatch. BAM ! super sword ultimate bankai power upgrade, fixed and better as new. Count the blades of Hihiou next time.
Maybe Kubo will go another way with Ichigo and explore his Quincy powers. (Can I call that convenient ?) So the half human, half quincy, half fullbring, half shinigami, half Visored boy can add that to his arsenal.
It doesn't matter if it was one or five pillers or that it just appeared, if they showed up before Soul Society was turned to rubble and the most powerful man (at least before those guys showed up) was killed like a he was nothing. Then they could've prevented something.
Even if they are the last defense, what good will it do if you wait and see how the second last defense is being blown away. It's more helpful to combine your strength. Now they have to help either way and rebuild the place.
About their strength, of course I knew those guys were going to be strong and they were named in the early chapters of the manga so that makes it less of an asspull. But it kinda disqualifies the rest of the Shinigami in one hit to fight in the coming arc. Byakuya and Kenpachi who were always 2 of the strong guys, got pummeled in their fights and are now in the shadows of five guys with more strength then the entire Soul society.
So unless that squad has very limited time to stay there, or some other handicap, I think some characters will really fall off the map and won't tag along in the next fights.
So I wonder, upgrades for everyone ? or will this be the 'Shippuuden of Bleach' and filter the rest of the guys who can't compete with the main shounen hero with 6 different modes that he never uses anyway.
Would like to see a very self conscious Kenpachi who looks at his sword and tries to understand his defeat in pure strength. He never cared about his sword so maybe unlocking a bankai would be nice next time.
