Explain It Like I'm Tree

Outline

The others start forcing the sadly abused van to lump its way on bent axles into the brambles, which grudgingly part for the rune-armored vehicle, but it's much slower going than Arthur running on foot.

Arthur makes his way into the now thoroughly haunted abandoned toy factory from hell. Lots of creepy setting stuff here, but when he makes his way deep enough, he comes face to face with... himself. Or, rather, a vision of himself with green skin and a manic grin over wolfish teeth. This is the creature that was last seen chasing Lewis and Dib.

I don't know yet how Arthur knows, but he knows this is not the cave demon that possessed him. He realizes pretty quickly that this is a projection of how Lewis saw Arthur right before dying. Let's call it Green!Arthur.

There may or may not be a minor beatdown of Arthur at this point. Green!Arthur threatens Arthur, saying he's going to kill Arthur just like he killed Lewis. Arthur throws him for a full loop by basically saying, "Yeah okay, on one condition. You'd better be damn sure killing me lets you move on, Lewis. Otherwise it's not worth it."

Along with the Halloweenish, haunted imagery that manifests whenever Lewis speaks, Green!Arthur is just the strongest manifestation of the angry part of Lewis that he was trying to suppress. Lewis absolutely knows Arthur was possessed in the cave, but Lewis is still angry and many of his other questions weren't answered when the group was sat down by Mystery (pre-story) to hash things out. He was just expected to accept the truth and move on. Now Green!Arthur is the part in charge, suppressing the rest of Lewis.

Green!Arthur recovers himself, and thus begins a lot of back and forth. I never did settle on whether Arthur answers standing stiff with his own fury up or if he is sitting on the ground in a completely defeated posture, giving the flattest, most numb delivery ever. The main points would be (not necessarily in this order):

"What do you mean, you'll let me kill you if it lets me move on?"

"If my life is what's tying you here and you'd be able to move on otherwise, you can have it. Get it over with. But if you're wrong? If you're not even sure? Killing me is probably going to turn you into something horrible, and you might never be able to move on. You might even turn on Vivi at that point. So THINK. Be sure. If you're sure, I won't stop you."

"You're giving up? Why?"

"I'm not even sure you're wrong to kill me. I was just possessed, again, and almost made to murder someone. Again. And this time it was a kid."

"Why did you kill me?"

"I didn't want to."

"Were you in love with her, too?"

At some point, maybe at this point, Vivi & Co finally catch up. Whether he was numb or angry before, Arthur basically screams at Vivi that if she interferes he will never speak to her again. He yells what happened was as much her fault as it was his, and if she has a speck of decency left she'll let him resolve this on Lewis' terms. He says something similar, but a lot less harsh, to Mystery.

Vivi is broken over this, but stays where she is, watching. Mystery, likewise. Dib is just recording like mad.

Green!Arthur is pretty surprised, because he knows he can't match the firepower of the rest of the team on his own. So he asks again, but his face looks less nightmarish as he does:

"Were you in love with her, too?"

Arthur doesn't look at Vivi, he looks at Lewis. He says that yes, he was in love with Vivi too. And, yes, there was an opening in his envy that he could feel the demon latch onto, but even in that instant it was too late to do anything about it.