Hello!

I am looking for manga that feature time capsules as something important to the plot.

When I say time capsule I mean the actual box/container where people (friends or classmates) put letters to themselves in the future, their favorite objects and whatnot inside, bury it and only open it years later.

I really want the capsule to be important. Maybe it has objects of a classmate no one remembers (20th Century Boys), maybe the story involves time travelling (Orange), maybe it hides dark secrets (Meisou Kuiki), or it is only opened after the destruction of mankind (7Seeds, Hotel). These are just examples, some of these manga don't even feature time capsules, but you get the point. It just can't be a passing event that doesn't really matter to the whole story.

Please, nothing ecchi, shounen-ai, shoujo-ai and their mature versions. I dislike "leveling-up" shounen. Already checked the categories and older topics.

Thanks in advance!

Love Hina how much such thing can be considered important in a comedy is probably up to you.
Edit: I missed you saying no ecchi, then sorry.

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What I like in Trivial Pursuit style. Pick your category:

its one of the one shot from Itou Junji Kyoufu Manga Collection, vol 12 ch6, titled In the Soil

Bouken Shounen, the 5th story.

Heptagon. Kind of similar to Orange, with a time travel element.

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世界のどこかに 必ず
キミの居場所が ある筈

Thanks for your suggestions.
I had already read Heptagon, but thank you anyways!
Please, do keep posting other manga