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. 
Why did you save me?
¿Por qué me ayudaste antes?
¿Por qué me has ayudado antes?
Por que você me
 salvou mais cedo?