Because Yukino's mom is a housekeeper for the Renjo familiy, she has to suffer the pain of hearing her mom praise the family she takes care of. And this is why Yukino has been trying to beat Renjo Tamaki for most of her life, so her mom would care more about her than the Renjo family. But when her mom gets sick, and she has to take care of the Renjo family instead, her goals change a little.
Also contains the side story "Kira Kira Suruhimade" in the final volume.