Tanabata is a little festival that is related in milky way.

the simple explains:
Hikoboshi meets Orihime at once in year.

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Originally, the episode from old China.

At once , Kengyu married with Orihime.
But, they didn't work.
Their behavior makes anger Tentei.
Tentei divided them so.

But, they can get permission at once in year.
That is today.
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Hikoboshi is same to Kengyu.
Maybe, Kengyu is his chinese name that he is the cow breeder.

Orihime is her name that she make clothes.

Tentei is most big god.
He is like the Zeus.
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But we write desire to paper and we hang it at bamboo tree.
I don't know how related in that episode :D