IsshinRyuuken. No Smoking in the Hospital Zone, Please and Thank You. The Hospital Administration.
It is no mistake that they both started smoking at the same time, and both gave it up at the same time.
Isshin sits and remembers forcing Ryuuken (not Ishida - not then) to share the last cigarette, despite the lack of 'hygenics'. He usually won that argument because smoking wasn't that hygenic to begin with, and Ryuuken really just fought for the sake of the image. They were supposed to be training to be doctors, after all.
They made a good couple, standing in the carnage of a battlefield, but when they left that scenery of raw honesty everything was a mess.
They fell in love. Got married.
Gave up smoking.
And then everything just started to fall apart.
When Isshin sat and watched Ryuuken (not Ishida - not now) smoke in the moonlight, he couldn't help but think that this should not have happened to their children.
But then Ryuuken passes the cigarette (so old, that mask of smoke that hides the lustful eyes and painful wounds).
And his eyes are scared behind his glasses.
Ryuuken snuffed the glowing embers out.
And leant in.