Just Fall for Me Already

Ai is just a plain old office worker. Only one thing- she's the adoptive daughter of the CEO and looks exactly like her daughter. After this started to get noticed by her adoptive mother, Ai would sometimes act in place of her sister Tokiko. One day, she's sent in place of Tokiko to spend time with Nagare Kuonji, the son of a wealthy entrepreneur, to buy time while figuring out what to do with an arranged marriage proposal. It was supposed to be a simple task to handle while everything gets called off, but it seems like he kind of likes her?? They shouldn't be doing this, but it just gets harder and harder to resist the temptation...
Source: MangaPlaza