There's a lot of evidence that goes to say we're not Kris' first captor/captive.
First of all, the cage in the wagon. They've had it since before we started controlling them, and they've likely had it for quite some time considering the beat-up condition it's in. Considering how hard Kris throws us into that thing and slams the door, it would make since that it's been used many times before.
Secondly, at the end of chapter one, when Kris exits the window after shoving us under a sink, Toriel states that Kris "does this sometimes." This is far from the first time they've done this.
Another note is how they do this without hesitation, and seem to fully recognize the outcome of removing their soul.
Lastly, Kris used to have a mind of their own when they were younger, but in the cutscene where Berdly talks about the spelling bee, where he, Noelle, and consequently Kris, appeared much younger, Noelle freezes up at December, meaning that she had dissappeared when Noelle was quite young. It's possible that Kris started acting up around the time when Dess vanished, since many of the scenes Noelle talks about where Kris still has a personality in general include Dess. I once saw a theory where it's that Dess is trapped in a dark world where she can't escape and is using Kris's soul to lead them to her, and honestly considering the evidence, it makes sense. But we aren't the first that Dess has sent. Perhaps the first one(s?) were unable to play their part. Perhaps they couldn't lead Kris the way that we can. Dess is the reason we don't have the vessel we made.
So basically, we can blame Chara after all. Just not for the things WE do when we control Kris.
