A blue box that's bigger on the inside

A one story house is all blue, and everything in it is blue. What color are the stairs?

Crazy couple got locked out of their home

a man eating his cousin's heart just outside said cousin's house

One person eats another persons heart out, it is implied that they are cousins

Someone killing their cousin

don't murder your cousins

An eye watching a violent swordfight.

the eye of ichigo