Ok, so we have 2 scientists with questionable behavior that are experts liars and twisters of truth that meddled in soul changing experiments.
So who was making those souls throw up to death?
I donīt think itīs Aizen, it would be too easy and i donīt think Tousen has turned to Aizenīs cause just yet and itīs very early for him to be making these kind of experiments, the first Hollows that were confirmed to be results from his research only appeared much latter in the storyline like the one that was about to kill Shuuhei or the one that possessed Kaien.
This is what it was said:
Doesnīt say much about the characters there yet the one commenting about the souls dissolving sounds a lot like Urahara when he was turning Ichigo into a Death God/Vizard.First person- ...I see.
First person- So an ordinary soul can't handle it properly...
Second person- How should we proceed?
Second person- Should we stop the experiments here?
First person- No.
First person- Let's continue this...
First person- ...just a little longer.
Plus this is the "worst possible scenario" according to him, now what would that be?