So i'm guessing kara is really the name of the big bad(the group named themselves after him/her/it) and the big bad has no physical form. That last page where koji was speaking about fearing kara and there's nothing you could do or whatever. It didn't seem like he was speaking on the group. It looked as if he was speaking on a higher power. I'm also guessing Kawaki is his body(kinda like orochimaru's jutsu). I'm gonna assume he is the last member of the Kaguya clan because his attack on the fatty looked like bone manipulation to me. It's not in color so it's hard to tell. But what stood out to me is that the bone hand(that's what I'm calling it) he pierced his chest with broke off. Just like when kimimaro would do the bone drill attack. Also when he chucked pieces at the fatty. It reminded me of when kimimaro shoots pieces of bone at people. Since kawaki is a hybrid human it's probably why it looks a little different.The Kaguya clan was like kaguya's clan or they were loyal followers who worshiped her. They're like a direct line to her I guess. We don't know too much about the clan or why orochimaru wanted kimimaru's body so bad(pause). So maybe that's why Kawaki's so special. He's the perfect vessel for such a being. Maybe "kara" is what kaguya was running from? It's obvious that kaguya's story has been saved and carried over into boruto. So maybe this is why we never got anything else out of this great clan. You know how kishi likes to drop a name and give it a whole panel. Then never speak on it again till waaay later with a big plot twist. After all this "vessel" talk I thought back on how kaguya came back to physical form. She actually used madara's body to make her return. I'm guessing this "kara" guy/girl/it has to do the same.