Movie about a girl saving her sister from an evil crystal?

I’m pretty sure it’s animated, if not anime.
It involves some kids that end up in this like big castle place with robots (I think?) which attack them under the power of this evil woman inside a crystal in a tower
And two of them are sisters I think. And then something happens and one of the sisters time travels into the future and there’s another kid in that time I think
and they go to the tower with the crystal thing to stop the robots and find her sister.
But when they get there, she finds out her sister has been taken by the crystal (after the girl disappeared from the past, I think) and that the old witch who was in the crystal is dead
that’s all I remember. There’s this dramatic scene at the end of the movie where the sister (who I think had been unconscious inside the crystal until this point) wakes up and stops the robots/castle from attacking the girl and the other kid and sacrifices herself to save their lives while the castle crumbles. I distinctly remember there also being a scene just before this where the girl and the other kid are getting injured while trying to make it up the tower stairs to the crystal.