This mirrors one of the most characteristic signs of Alzheimer's — repeated questions and statements: unable to retain what they have just said or asked, a person will repeat the same words again and again, entirely unaware that they are doing so.
And that is the heart of the design:
He doesn't know he's repeating. You're the one who notices.
At seventy, Yuki can't return to the present. Recent memory is going; distant memory remains — so he goes back, over and over, to those nights between 1989 and 2019. To him it isn't repetition. It's the part he can still reach.
You stand outside the screen and watch him pick up that photo frame for the fourth time, and say the same line for the fourth time: "He poured so much into writing these — and so much regret."
That gap in awareness — he has none, you have all of it — is where the whole design gets its weight.