Manchu (满族）started from a branch of 女真. Another branch of 女真 in the 1100s to 1200s formed the Jin Dynasty after defeated the 契丹 Liao Dynasty in Northern china . Liao in terms of sinification went as far as claiming that they were the descendants of mythical Yellow Emperor, and at other time, the other mythical Yan Emperor. The good folks in Song might have a problem with that claim, but in all fairness, Huang/Yan Emperors could’ve had many progenies.

Initially the leading 女真branch in the 1600s called themselves 后金, as the later version of Jin in the 1100s to 1200s. But after they united the area covering now most of the current Northeast China, a portion of Russia and a portion of Korea, they abandoned the name of 女真, and include many Mongolians, Hans and Koreans in the united area, call themselves 满族. In that sense, Manchu started as a very inclusive group.

A couple of points to make:

* Sinification is more of an infusion process, and Chinese culturally is ever evolving. If you had a time machine to port a Zhou “Chinese” to Han, or a Han “Chinese” to Tang, or 王夫之 to modern day China, certainly there would’ve been a whole lot the old “Chinese” had had issues with the Chinese-ness of their descendants.

* Han historically as an ethnic group, in a way is the total opposite of what whites were like in the new world until recently — you were considered a Han so long as,

1. you have a drop of Han blood — at the very least, paternal side of it.
2. you have converted culturally.