Cat Grabbing Kitten by the Neck

I am four and a half weeks into my male year old cat and my ten week old female kitten's introduction. They are separated at night and when I am away. Every time they get together, after a separation, (mostly after the night separation) she runs to him and sometimes purrs. He grabs her by the neck and pins her down. Sometimes, she continues to purr or he may nip too hard and she meows. She then scoots away or I have to get on to him with words. They then will spend a lot of time chasing each other. They will also play where he turns over on his back and she attacks him. Once in a while, he will do the pin down and nip or will chase her and pin down and nip. This often has no explanation as to why he turns like this or he seems to be done playing. It's like he has times he loves having a friend and other times he wants to beat up on her. On another note, he seems to be perfectly fine with her eating his food or drinking his water. He is also fine sharing a litter box. By the way, this only happens sometimes because they have their own boxes and bowls.

What I can't figure out is why he starts the morning like this or gets ugly, but plays other times. How should I interpret this?

Is he neutered?

Yes, he is neutered. The odd thing is, this morning, his "first of the morning neck grab" was worse than usual. Had I not been there, she may have been really hurt or worse. This neck aggression is only after being reunited in the morning, after being separated.

It's odd. It's like he wants to play and then has times he wants to get mean. I don't get it. They have been together four and a half weeks and I am wondering if supervised visits will have to go until she has some size on her. That could be a few months.

I was hoping someone else with more integration experience would chime in.  I'm wrestling with introductions of my own.  It sounds as if he is just asserting dominance over her which is okay, I think.  As long as he isn't hurting her and I think you are wise keeping them separated until she can defend herself if need be.  One of them will have to be the dominant cat and he is telling her he expects it to be him.  It can work out okay because she is so young she will probably go along with it and will give him the respect he is asking for.

Are you planning on spaying her at 16 weeks?  Or is she already?  If she is allowed to go into heat all bets are off.  Hormones change them so much.

Dandila said:

 
I was hoping someone else with more integration experience would chime in.  I'm wrestling with introductions of my own.  It sounds as if he is just asserting dominance over her which is okay, I think.  As long as he isn't hurting her and I think you are wise keeping them separated until she can defend herself if need be.  One of them will have to be the dominant cat and he is telling her he expects it to be him.  It can work out okay because she is so young she will probably go along with it and will give him the respect he is asking for.

Are you planning on spaying her at 16 weeks?  Or is she already?  If she is allowed to go into heat all bets are off.  Hormones change them so much.

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      I agree with all of this.

Introductions can take ages, and at least they are getting on most of the time.  If you're really concerned you could go back to the whole formal introduction technique