He spent most of his time when at home studying the cats behaviour. It surprised him how much pain it was in, physically in mentally from losing her babies, yet she didn't really show it.
It was probably from spending this time with the cat that it began sleeping on Kazuo's bed. It didn't bother Kazuo, in fact, he made it a nice comfortable spot on the bed just for her.
Now the only problem was that he didn't think he would want to give Yosuke the cat back. He even feared that his mother would go on her rampage when looking for drugs that she would hurt the cat, so whenever Kazuo heard her making a ruckus, he would keep the cat near him.
Perhaps the oddest of all Kazuo's new behavior towards something living that wasn't his brother was the fact that Kazuo would find himself smiling at the feline companion unintentionally. He just found it...well to put it simply: cute.