Ha! I know I spotted this before anyone: Okami AR!

[Zetta]

In the game Okami, there is a charater named Sakuya, a tree sprite. She is linked to her tree. When the game starts, she is tall, statuesque, and buxom, clad in a green outfit cut to show off her breasts and butt (Basically, peach shaped holes showing very pink cleavage, and most of her ass.). After a certain scene, though, she gets rejuvinated, her tree going from nearly dead to vibrant green to bright pink peach blossums. When you see her after this scene, she is weaing something much more revealing, but she's considerably younger (her breasts are smaller, for one thing). I don't know yet if she gets even younger though. (I don't have any way of putting this online, so someone else will have to get it.)