From Animeraider:
When 16 year-old Haruna runs away from an arranged marriage, her parents force her younger twin sister Wakaba into the marriage instead. But while Haruna ran off with a boyfriend, Wakaba has never even been kissed. How will a high school girl survive going from nothing to full on marriage with no steps in between?

Every day Sakuta Gotou likes to zone out to his favorite band, Incest, because it makes him feel at ease. However, this band is very secretive and has yet to have a live performance. Now, when the chance comes to Gotou to see his idol Iive, the band's singer, on stage, he finds out that she is the new transfer student in the classroom next door... and to make this even better she stops the concert and grabs him saying, "I've wanted to see you." What is he going to do now?