Kanetsugu Gasou

Kanetsugu Gasou, a boy born to an originally rich family that lost it's wealth, is a chubby guy who introduced himself to Adagaki Aki as her childhood friend Masamune. He shocks the Adagaki's household by showing them a marriage proposal certified by his father, an old friend of the Adagaki's head of family. Henceforth he shall have an arranged marriage Adagaki Aki.

[Spoiler] It turns out that he isn't actually Adagaki's childhood friend. After being mistaken for that person Gasou lied about his identity in order to get close to the Adagaki household. He hopes to fund health care for his sick sister using the capital of the Adagaki family. [/Spoiler]

[Spoiler] It is later revealed that Gasou is female and tried to hide it for the sake of his scheme. [/Spoiler]