Barairo no Ashita

The first guy Rika ever falls for turns out to be her older sister's fiancé. However, her sister's dream since she was a child was to be a bride, and ever since her engagement to another guy didn't work out a few years earlier due to her not being able to conceive, Rika swore to do everything in her power to help her sister fulfill her dream. Does that include helping her marry the guy that she's in love with?!