- Similar to Ainz from Overlord, his biological body also affects his mind. This is mostly the main reason
- He wasnt even morally good even when he was human from what I've seen
Also what do you mean cat gore just because?
- This wasn't exactly explained before. It can be assumed, however there isn't any confirmation so it could very well be that he was already like that, but we don't know. In Overlord there are multiple instances where this is clearly indicated, both by Ainz himself and by the "calm spells" auto activating when he gets emotionally unstable.
- Where did you even get that from? There was nearly 0 information about his past life up to this chapter at least. All we know is that he liked to play this game.
And it is "cat gore just because" simply because if he could have gotten into her room, which seems to be where the cat was at the time, he could have just killed her while she sleeps. He didn't have to kill the cat at all, and did that just because he wanted to with a ridiculous excuse of it being to get to her.
I didn't read past this chapter, but his "strategy" seems absurd. If she suddenly found her cat dead, wouldn't she be more alert and start an investigation to find out who/what did it? Imo that is a horrible move either way.
Trying to get another skill would at least be a better justification than that, but I'm pretty sure this wasn't even mentioned as part of his plan beforehand.