Under the Dapple Shade

[From AnimeNewsNetwork]:

Tending to his sister, who is paralyzed after a fall from a tree, Tatsuya Kitazaki wants revenge. Yet, just as he is about to cut down the tree, a strange and seemingly ageless girl, Sara Nishikujo, appears to stop him. What's more, the girl seems to have the ability to communicate with plants - and she tells Tatsuya the tree's version of his sister's accident. This marks a watershed in Tatsuya's life, as everything begins to change.