Kanako loses her father due to an abrupt accident. Because of his passing, the massive debt the company he once lead is left to her. She had no time to grieve. Her mother had passed away when she was a child, so she no longer has any relatives she can rely on.
When she was completely at a loss, a saviour extended his hand for her to hold...The hand belonged to Shingyouji Souichi, a representative belonging to a large enterprise. He apparently was an old friend of her father's.
Souichi had quickly repaid the debt, started a new business, hired all of the staff from her father's company, and on top of that, officially became Kanako's guardian.
Set to live in the Shingyouji family's main home, Kanako gets picked up by Hayama Tsukasa, who was her father's secretary, and is lead to a location appointed by Souichi. She finds out that it's not the Shingyouji mansion she'll be living in, but in an apartment where his two sons live on their own.
Instructed to cohabitate with the brothers, Kanako felt uneasy. During her unease, Souichi mentions something that kicked her further down...
"Choose one of them to marry. Whoever you choose will take over my company."
Thinking of how much Souichi had done for her and the employees left over by her father's company, she couldn't refuse.
Little by little, not even Kanako herself has realised... that she's slowly being lead into a birdcage...
[Translation of the official website's plot summary.]