Come on in and mind you don't kick the dog's water dish here at the left. In Japan, once you enter the genkan you are still officially outside until you actually step up. There is always one step up from the genkan. This is to separate the outside from the inside. It is customary to actually remove your shoes before you enter a house.
Shoes are dirty, they make the floors and the tatami mats dirty.
Just grab a pair of slippers and come on into the kitchen. Actually, on my way to work, I usually forget things after I have put my shoes on. So I ignore the rules and sneak in with the shoes on. Of course Mayu gives me shit. But we try.