Niina Isokawa

Nna is a blondhaired girl who goes to the same class as Marie. She has an American mother a Japanese father and a great deal of energy. She039s very busty for her young age and is physically very active and extremely friendly quickly attaching herself to Marie to the latter039s initial displeasure. In the manga she has a crush on Yuji who is torn between her being underage and her ample bust and often refers to him as oniichan. Wikipedia