Love Hina: Totsuzen no Engeji Happening

After having failed the Tokyo-U entrance exam, Keitaro Urashima is nowhere near achieving his goal of entering Tokyo University and meeting his fabled "promise girl". Or is he?

After catching a glimpse of his latest bad scores, Granny Hinata decides to send a real Tokyo-U student to help Keitaro, Naru and Mutsumi pass. Her name is Mizuho Fujisawa and she bears more than a passing resemblance to the girl Keitaro made a promise to several years ago. Furthermore, she is so confident that she can get Keitaro to pass, that she makes this wager: If Keitaro can't pass under her tutelage, he will get to marry her.

Just who the heck IS she?