"He used his own bloodline as the primary restraint, merging and absorbing all the power of the Tainted to create an entirely new power.
It was... a bloodline power called the Sharingan. Indra completely integrated all the power of the Tainted into that new bloodline power.
Indra's thinking was that, since one person could not bear the combined power of these Tainted, he would continually dilute it and pass it down through his bloodline.
However, the Tainted varied in strength after all, so Indra developed this bloodline power further. The weaker Tainted were drained completely and became the foundation of that bloodline power.
The slightly stronger Tainted were repeatedly scoured into seeds, hidden deep within that bloodline, waiting to be awakened. As for some of the even stronger Tainted... after making certain contracts with him, they too became seeds, each carrying Divine Techniques of 'Divine Authority,' the essence of gods.
However, this method also caused some minor side effects. The power of the Tainted that became the foundation of the bloodline power would indirectly affect the emotions and thoughts of those who bore the bloodline.
Although the influence was not particularly great... the further they developed their bloodline power, the more power of the Tainted they would bear. Naturally, the influence on them would also grow stronger.
However, as time passed, the power of the Tainted was completely absorbed by Indra's bloodline and became its own power. As a result, the power affecting their emotions also weakened somewhat.
As for me, I was among those who made contracts with Indra, and our contracts... never mind, let's leave that aside for now. What you need to keep in mind is this.
Not all the Tainted in the present Shinobi World were absorbed by Indra. Many became Fallen Gods again.
And they