RION has a little sister named Yuki, which also has a boyfriend younger than her. But RION finds the little dude so cute. So she starts to seduce him with her huge pair of humongous boobs.
Initially, Junior-kun loved Yuki, a plain as a table young girl, but after checking out big sister RION tits he acquires a newfound taste for big tits. Plus RION prancing around her tits without any bra is a wake-up call for him. He and RION start an affair literally under the sister’s nose.
The story is simple yet funny. RION looks hot… really hot