After a fight Hayate, Nagi heads to the apartment complex to hang out.  But her “little sister” is the only one home.  This might be Nagi’s chance to find out what Ruri’s real goal is. 
But we don't know anything 
about each other, so...
Pero no sabemos nada el uno sobre el otro.
Pero no nos conocemos ni sabemos nada el uno del otro,
Mas nós não sabemos nada 
um sobre o outro. Por isso...