His happiness on the last page.
Reminds me, if anyone wants an interesting read on end-of-life care and the process of aging, I'd recommend the book "Being Mortal" by Dr. Atul Gawande. It ties in a lot to the themes of sickness in old age in this manga; especially regarding how we treat death as a failure of modern medicine and not an inevitability that everyone will have to go through.
Because of this, we hook up our elderly to all sorts of machines in stark white hospital rooms, chaining them to an abysmal quality of life, when there have been studies that indicate that patient outcomes are actually better when they are allowed to be in a place they feel comfortable surrounded by people they love, even with less intensive medical care.