The girl I love is my brother's ex-girlfriend. She's a trashy girl who's clingy, stubborn, and takes advantage of my weaknesses. But I can't seem to stop our relationship.

Kouki and Nao are siblings that harbor feelings for each other that they're not allowed to express since they're 'twins'.
"I locked away the key gently in my heart but mom reveals a secret about Kouki!"
"The person I like is my twin!" Pure 120% romcom, start!