The content is that a guy has been doing something (painting some words) on the tree due to some reason. He kept doing that then he met a water goddess inside it. Then after some time he learned that he has been doing that to seal the goddess in the tree.

He learned that the goddess has fallen in love with his ancestor and was trapped by him there. Then he tried to unseal the goddess there. When he was pierced by an arrow, the goddess thought he was gonna die then she went berserk.

Do you guys know this manga? Please help. ^^

I'm pretty sure it's Otogibanashi no Fude, an oneshot.

Thank you so much!! You're right! That's it. Thank you, thank you~