User blog comment:All fictions/What do we know about esper powers?/@comment-25364614-20150430123029

A nice round up of observations there. Certainly its one of the biggest mysteries in the franchise and another example of deception used by Kamachi in the series: it seems to be the most easiest to understand and ubiquitous concept in the series but it has more mysteries than the concept of using magic does.

Another quote from NT7:

''“You don’t get it? That’s #028. That’s the previous Rensa. To get technical, it’s a human hypothalamus that was chopped out and repackaged. You could say it’s the smallest unit of life. Not even Academy City’s tech could mechanize this part. Of course, that could change at any time.”''

“You can’t mean…”

''Kamijou was at a loss for words. Fremea screamed and Rensa seemed to enjoy hearing it.''

''“It began with that failed project using the #3. A clone had the exact same physical body yet at the same time functioned as a distinct human being. It seems one of the great mysteries of life is the fact that life forms gain the role of the master when they are created. That gets in the way of acting as a pure slave in order to become an output point for esper powers.”''

And so they had shaved away pieces of the human body until that “mystery of life” was gone.