Board Thread:Theories and Speculation/@comment-30323490-20170305205254/@comment-734582-20170306110447

BlazeRelease wrote: I mean they might as well be able to choose who they reincarnate to don't you think? Hagoromo directly says that "Ashura chose you" so yes.

The Senju and Uchiha were the most powerful clans in the world, and they are the most direct descendants of the two transmigrants (as well as having numerous transmigrants). So i guess it's a bit of a self-sustaining level of strength.

Nevertheless, hashirama was a transmigrant and his cells were coveted. Madara was the second most powerful shinobi, and also a transmigrant. Naruto is now the most powerful shinobi and a transmigrant. Sasuke, the second most powerful shinobi is also a transmigrant.

What i was thinking of however was wood release and the Rinnegan. Hashirama is the only natural user of Wood Release. Only two transmigrants can form the Rinnegan.