Be Missed and Remembered: The Letter from Mayoiga

The setting is 50 years ago, 1972 (Showa 47).
The protagonist, a high school student, is heading to his grandparents’ countryside home.
A short trip taken during summer vacation, a yearly tradition.
Spending time with his sister, peacefully interacting with the villagers, but…
"Do not enter the mountains. You will be cursed."
There seems to be such a legend in the village.
People believed that monsters lived in the mountains, and if cursed, terrible things would happen.
“The era of moon rockets — it’s completely unscientific.”
The protagonist doesn’t believe it at all, but there’s another reason.
He had actually seen the monster’s lair before.
He knew it was just an old shrine.
Without hesitation, he set out again toward the forbidden place.
Walking through the countless torii gates that stood exposed in the mountains,
He finally saw the old shrine rising from the lake once more.
Without hesitation, he entered the shrine, but then a strange question arose.
…Why hadn’t I entered here before?
Having come this far, he should have gone inside, but for some reason, he couldn’t remember anything from that time.
“Looks like you’ve grown taller?”
A voice rang out.
He recognized the voice’s owner.
More precisely, it was something he remembered once inside.
“…How many years have passed since then?”
“Five years and three days.”
We met again, after 1827 days.
Neither of us bothered to ask for names. We already knew each other.
But this “knowing” wasn’t something guaranteed for the future…