Overview:

Her parents go on a business trip overseas, and she begins to live alone with Kurumi, her sister-in-law.
Kurumi is an energetic and bright girl who loves playing pranks.
She plays a lot of cute and naughty pranks on the virgin brother.
Although it is her in-law, as an older brother, she must not be lustful towards her sister.
However, the older brother succumbs to the temptation of cute Kurumi, and the line between brother and sister…