Nii-san, step aside! I can't kill that person!!
"That person" being annotated as "Kirino", of course.
It is a parody of "お兄ちゃんどいて!そいつ殺せない!" ~ S-Ken Tsukimiya(S県月宮) incident reference.
It is a famous internet urban legend about a player of Ragnarok Online troubled by a paranoid stalker girl.
