OK. I need to update my comment from the last chapter from "considers her sister a pest" to "considers anyone BUT Ume to be a pest". Still cute though...
Before asking "what should I do?", the question you should ask is "Did they sell/give her away?". If they did, then the answer is simple... BEEP THEM!!
It not ridiculous. Friendships in real life can be easily broken cause of personalities. He has stated he doesn't like airheads, which she has shown she is from her ideas. They are currently friends cause they are both reincarnators, so the question becomes "how long can he stand being with her?".
While I don't agree with her method of choice, I at least understand the point she was trying to make. The hydra might be as strong as a demon. So if they can't handle a single hydra, what makes them think they can handle the demon army? They might as well just grab some random stick off the...
Can see the picture in the last page. Ether it was made before she was born or that refused to include her, which would make sense with how they act towards her....sad.