Register address at my someone else’s place

Hi,

Is it possible to register yourself at someone else's address?
I need to have an address registered in the first 14 days I arrive in Tokyo for my employment, but I will have to stay at my girlfriend's house the first three weeks because I have no other option.
Is it possible to go there and register myself, then change three weeks later? Even if I am not the one renting the place but my girlfriend is? Do I have to talk to the landlord first? I don't want him to raise rent on my gf or anything of the sort.

Thanks.