The Younger Brother, often thought to be named Naiee (spelling may vary), is one of the two protagonists in Brothers: A Tale of Two Sons. He and Older Brother embark on a journey to save their dying father with the Water of Life.
Younger brother appears to be around late tweens/early teens of age. He appears to be somewhat lanky, with his skinny build. He has a head of bright yellow, mop-like, messy hair, as opposed to Older Brother's neat brunette hair. To contrast Older Brother's color scheme, Younger Brother has an orange and brownish color scheme, with a patched shirt, vest, and pants.
As one can probably expect, Younger Brother is mischievous for his age. Interacting with NPC's reveals he likes to have fun by messing around with people (dumping water, playing with a broom, messing up the straw on someone's roof), and is overall a playful boy, as indicated when he plays rock-paper-scissors with the Inventor. He appears to have some skill or talent at playing the harp, as well. It can also be assumed that he has a liking for animals, as shown with a cat and the Gryphons.
But underneath Younger Brother's immature exterior, one can interpret he's not completely sure in his abilities, and believes it's his fault his mother drowned. As such, Younger Brother is unable to swim, and a near-death experience shows he's afraid his brother will beat him up.
However, Younger Brother, towards the end of the game, grows up to face the final obstacles to reach his father. His determination from what he'd lost gives him the strength to do the things he couldn't do before, such as pull the lever, climb the tall ledge, and most significantly, swim without anybody's help. By the very end, it's shown that he's matured greatly from the experience of his journey, as he'd shown stoicly mourning at the graves, consoling his father and keeping a straight face.