I know for others the way the sister acts is normal but I think it's too much? I'm also get scared of the way she acts like... she has no remorse or control to her desires, did she even felt guilty of killing her brother "accidentally"? Maybe she does but I can't see it.
I mean I don't like her but they're not really dead. She might be feeling a bit guilty to hit him so hard that he ended up in the game, while being in a comatose state, but she's too much of a fan of the story to really care.
She's probably there to add comedic affect but it's so annoying, really. #-.-)
Did he die because of the sun or because he reached the immortality expiration date?
He died of old age and he wasn't immortal. He said no one lives forever.