Joshi Kousei

Ryota Kobayakawa and his little sister Ami got along like oil and water.
Now that she was going to his school (and popular, too!) their home rivalry now extended to the classroom.
Likewise, whatever problems they had at school, they brought home. There was no reprieve.
One day Ryota and his friend were checking out a "maniac" porn site on his phone.
Among the nameless pretty girls doing weird acts he recognized Ami. His sister is into this stuff!?

[From DLsite English]