Oniichan, gacha - Elementary school student Miko was born to a poor family. Made responsible for all the housework by her mother and siblings, she hopes to escape from the harsh reality. One day, Miko inserts a coin to play with 'Oni-chan Gacha', a vending machine which dispenses toys in plastic capsules. She turns the handle as she wishes for a kind brother. Her world undergoes a drastic change from that day on. Older brothers who are like fantasies, appear before her one after another.