The Young CEO Dotes on His Fiancée's Older Sister

https://www.cmoa.jp/title/328000/
Mio has been treated like a housekeeper by her stepmother and younger half-sister. She is trapped, unable to leave the house. While her sister boasts about her many marriage interviews, Mio has none. One day, a single marriage proposal arrives for her. Her potential suitor? A company president.