Capital is resources needed for production of value.
And that stack of decade-old manga is a resource that might indeed provide value (in the form of continuing enjoyment) to a manga collector. That makes it capital. A $20 bill in my wallet is ultimately a claim on real resources that the central bank commits to honoring, by preserving the value of the currency—that makes it “capital” from a strictly individual perspective (indeed, such claims are often called “financial capital”), although it’s indeed not real “capital” in an economy-wide sense (because any such claim must be offset by a corresponding liability).
And that stack of decade-old manga is a resource that might indeed provide value (in the form of continuing enjoyment) to a manga collector. That makes it capital. A $20 bill in my wallet is ultimately a claim on real resources that the central bank commits to honoring, by preserving the value of the currency—that makes it “capital” from a strictly individual perspective (indeed, such claims are often called “financial capital”), although it’s indeed not real “capital” in an economy-wide sense (because any such claim must be offset by a corresponding liability).
Sigh. You can, of course, define any word any way you like it, but I have my doubts about the usefulness of such endeavours. Go read).