Fuku

was once a beautiful, thin princess that highly resembles Ino Yamanaka.

Background
Thus, when she stresses about meeting her new fiance, Prince Chikara of the Land of Udon and gains weight, she enlists the help of Ino to impress him.

Part I
She hires Ino as a body double for her as she once resembled her to make Prince Chikara fall for 'her'.

Princess Fuku is very stubborn, absolutely set on her plan working despite all of its flaws, and is very hard on Ino and Naruto, who comes with Ino to assist. In the end, her plan fails when she is revealed to Prince Chikara, but the Prince likes her new physique and the engagement is confirmed. Ino and Naruto then return to Konoha, pondering the strange events.