Senku could get to know more people. That's what the communication devices are for, among other things. He's smart enough to know that, so Tsukasa doesn't need to say it. They started small in the Stone World. Revival fluid took time. Even though these people are alive and well, awake and their semi-natural selves, he already has more people than he had after six months in the stone world.

"If I end up as a kitten, I will show you why no one should take any felines for granted."

Not by harming Senku. He'll never harm Senku again, not even if it's the last thing he does. Tsukasa drinks some tea, amused at his own words. He doubts he'll be a kitten. Perhaps Mirai would (if she can't be a mermaid). She might like it here if she can be a mermaid, but he doesn't trust the fox with her. Better she's safe. He can live here without her.