Pretty good update.

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The guess that Sera can overcome John's "Anything you can do, I can do better" power by hers being effectively invisible was correct! But I think it's fairly cool how John combines the powers he's copying into novel forms, such as using Cecille's to give Arlo's barrier spikes.

But the psychological element is more interesting. John is convinced — has been convinced — that he is nothing more than who he is on his worst day. And because he needs to believe this, because he's decided it's the axiom of his life, he's stuck in a funhouse mirror world where all he can see is that people are just like how he sees himself. If he acknowledges that other people aren't all complete monsters, he'd see himself as incommensurately worse than the rest of them, and quite possibly try to kill himself if my read of the end of this episode is correct.

There is a way out. He can realize that the John who became Sera's friend, who was nice to anyone who would be nice to him, and make a spirited attempt even at befriending those who weren't (see: Sera at the start) was him too. He may have done some very bad stuff, and currently be engaged in doing more, but that's not all of who he is, and it's never too late for repentance to make a difference.