Your life as a lonely bachelor was terribly boring. Every day, when you came home from work, you found yourself at your empty apartment... Until recently. But recently, your little sister moved in with you! She entered the middle school near your house and now lives with you!

Another evening. You walk through the door of your apartment. A cute girl in a seifuku runs out to meet you. In her hand is a ladle, and on her face is a cheerful smile:

"Onii-chan, welcome back! Do you want to take a bath? Or dinner? Or..." Lumi's smile becomes teasing "...me?"