Board Thread:Questions and Answers/@comment-30535075-20170130152405/@comment-5398287-20170130223144

It looks like Rukia came through a portal of some kind rather than phasing through the wall. Spiritually aware Humans can physically interact with Souls like Rukia.

The bit about the massive amount of spirit energy was referring to the massive amount of Reiatsu present in Fake Karakura Town due to all the upper-tier combatants fighting each other.

As for your reply:

He's referring to the Shin'ō Academy, the general school for Shinigami.

I've always been under the impression that the act of gaining Bankai, not activating it, increased one's power by 5-10 times, but yeah, it's probably in that range for the Arrancar and their Resurrección, given how hard the tables usually turn when they activate them.

The Shin'eiyaku were sent to all the Shinigami capable of Bankai. At that point, Byakuya was probably still in the Soul King Palace/falling toward the Seireitei, and Kubo likely wanted to keep his new look a secret until he came back for real, so he just didn't show Byakuya taking the pill. There's a panel in 554 of As looking up into the sky as though the contents of his Medallion just went up there, which implies this scenario.