Our protagonist, Takuya, was attending university, but despite his efforts, he failed a year.
Since then, he became a shut-in and obsessed with the "live streamers" of Nukinuki Video, girls who broadcast and comment on their lives.
One day, he realized that a popular streamer with her face hidden is his younger sister.

Not wanting her parents or school to find out, the sister did whatever the protagonist told her to do.
And so the protagonist's rampage began.

[From Getchu]