My kitten hates the new kitten I adopted?

Since Ninja was the first one to live in your home, it's normal that she wants to protect her territory. For the other one it was easier to adapt to live with another cat because when she came into the house Ninja was already there. You just need to wait, they won't probably really fight, and in a couple of weeks (probably sooner) they'll be playing together. And trust me, they'll be more likely to hurt each other when playing than now, so cut their nails!!