You have to remember that Hikkis "First Love" album sold 9.5 millon copies but then it's been lower sales for the rest of her albums, about 5 million, maybe for the Deep River release some of those 9.5 million people decided too buy it. I think Ayu is releasing too much material and people dont' have money or something too buy everything she releases.Or it could be that Hikki has more fans.
HIKKI RULES!!!