Why do light novel protagonists always brag about having cute sisters?

[Agent Abe Caprine]

Japan, please explain.

 

[Napoleon Bonerfart]

Rape kits fail when centimeters are involved.

 

[Vingle]

Incest is wincest, you gotta respect the difference in culture. Ya bigot.

 

[GorillaGhost]

I think my sister is cute, but I'm not attracted to her. You can think anyone or anything is cute without being attracted to it. Don't you think puppos are cute? Do you want to fuck puppos? If so, you should neck yourself.

Only a coombrain moron thinks everything revolves around fucking. Don't be a coombrain moron. Also, I'm glad my sister is not an ugly, fat slob. Ugly, fat slobs make everyone around them miserable. So don't be an ugly, fat slob either.

 

[augment]

Upon reading that the main character has a cute sister, the reader, who is fat/unkempt or lonely (or a combination of the latter) will activate autonomic preganglionic neurons within the spinal cord. Penile erectile tissue is thus estimulated, vascular pouches given the go-ahead to engorge in blood fluid. This sends a direct response to the reader's medulla, pons and diencephalon project directly onto spinal sympathetic, parasympathetic and pudendal motoneurons.
Thusly the reader decides to not only keep reading, but to consume more of the same material.

 

[Lucky Jim]

Because of course if you can invent fictional people you're going to make them ugly