The Phantom is here... But who is he?

The Phantom Arc

The Captain and Commander returns after a 5 year long mission. beaten down, old and dying, he addresses an issue about Shinigami death tolls. It greatly threatens the safety of not only the citizens of the soul society, but the shinigami society as well, so Hanzo thought it was wise to put an end to it and so he summoned all captains.

With a letter from Hanzo's deceased Vice captain, it states that the hollows have grown smarter over the past few months and were multiplying in an unbelievably quick phase. He was one of those who survived an investigation, but later died, or rather, murdered to keep silent of the matter. Of the hollows were growing smarter, someones making them so. But who is this 'someone'... Is he a friend or a foe, what's his purpose, they all wanted to know.

It was days later when a 3rd division recruit sent Hanzo a letter from a person who called himself the Phantom, he ignored the letter and its contents despite the fact that it came from the 3rd division, it was not later that day that the same recruit killed her self. Upon hearing of the news, Hanzo realized who this phantom was...