(sorry cuz this post is a great big massive wall of text
also ****'s gonna go down in 3... 2... 1...)
Luna saw the bright light coming out of Izzy's bag. She knew that it could only mean one thing - that Liam was about to regenerate. Quick, get the knife and give the gem to me! I'll distract him or something, and you can kill him again! she thought to her sister.
OK! she thought, doing what Luna told her to. As she handed over the gem and got the knife out, she saw a white blob float out of her bag and upwards. It formed into the shape of a person, and after a few moments, the light disappeared.
Liam saw two girls standing in front of him. If they were just two girls he'd never met before, he would have been feeling fine. He'd probably try to annoy them, or try to get along with them to gain their trust, then steal their gems when they were asleep or something. But the two girls who were standing in front of him were none other than Izzy and Luna.
He knew Izzy was very likely to want him dead after what he'd done to her. After he'd annoyed Izzy when they first met. After he stole her gem. After they argued several times until eventually they began to hate each other. After the fight they had, which ended up with Liam having to kill her to stop her from killing him.
Of course, he'd done some things that made Luna hate him as well. And if how desperate she was to find her sister was any indication, she cared about her sister a lot. Which meant that she probably wanted him dead too, because of what he'd done to Izzy. He also did some things to Luna. He stole her gem, too. And when he fused his gem with hers, he freaked her out to the point where she thought she was going insane. Sure, he had explained to her afterwards what was going on, but he had to lie to her about stealing her gem. Not only that, but that had happened after he killed her sister. He had to lie about that, too, and lied about having Izzy's gem. And once she'd found out the truth, he tried to kill her as well.
Liam wasn't scared of much, but seeing Izzy with a knife (the same knife he used to kill Izzy and attempt to kill Luna, in fact), and Luna with hers and Izzy's gems that had been fused together, terrified him. He didn't care about that fact that he could regenerate if they killed him. He thought they probably hated him so much that they'd try to find a way to make sure he never gets brought back to life again. Before he'd thought that they probably wanted him gone for good, but now that he had noticed Izzy's knife and the expression of pure anger on their faces, he knew for certain that they wanted him to die. And they were going to be the ones to kill him.