...Shit. I had a bad feeling you were going to say that. [There's the hint of a mental sigh.] But... Thank you for doing what you can. Even if the medicine can't cure it, at least this will make it easier for him to fight back against it.

[Eren's father was a doctor. He might not have learned much about health and medicine himself, but Eren has seen firsthand that sometimes, some things just can't be cured and there's simply nothing that can be done about it. He also has a vague idea of how much having the right kind of medicine can still help. Although if Armin will need this medicine indefinitely, that does create another problem.]

How hard is the medicine to make? Do you think Liminal Manipulation would work?