Satou Fuuka is an orphan. Her aunt, who was her guardian, absconded in the night, leaving her with no money. Her parents wanted her to go to school, so she was looking for a job to cover her school expenses and rent (plus living expenses, though she didn't mention it). She goes to be interviewed for a part-time house helper job but is rejected before she can say anything, because the guy offering the job is the eldest for 4 brothers and it's an all-male household. She pours out her story, so he takes pity on her (even though he'd pointed out that she can't really take a part-time job if she doesn't have a guardian) and offers the job as a live-in position. However, he has one condition: she's supposed to disguise herself so his brothers don't take an interest in her. Her disguise: lots of towels around her body, so she looks fat; makeup so she looks old (39); plus her hair is all loose and she's wearing glasses.
The brothers are: Tsukasa (eldest, apparently already working); Akari (second son, first year college student with a wider strike zone for women than Tsukasa thought); Kairi (third son, genius high-schooler and Fuuka's classmate); Minato (youngest, first year middle-schooler who's a blue-eyed blond). Incidentally, Fuuka notices that none of the brothers look related.