The problem is that Thanatos does understand, and all through his time on the train he's been told that he has to learn to live without what's important to him, what's a part of him, what he wants. He has to struggle every mission because who he is doesn't matter. Despite everything, he is still Death Incarnate. His duty is important and the reason he exists, and in the end, he hasn't been able to be himself for five months now.

Thanatos doesn't know who he is anymore. He can't be that, but he can't let go of it either. Nothing is right, and everything is wrong or uncertain. And now... the reassurance that there are other ways Ryo can help, to relate their struggles, and show concern like Ryo has shown him multiple times isn't working.

Rather than trying to push the issue, Thanatos opts to stop before he makes things worse. He's been good at that, and he's only just starting to make amends with some of it.

"That's not my point either," he says calmly before shifting away... or as far as he's able, and he doesn't stick his landing. The message remains the same; he's done with the conversation.