Responses
I think when he said 'why is she here' he meant the black haired girl? Idk
I thought so too, but after that he said "that person?" as if he had just noticed the girl next to Suzu. Not to mention Suzu is primarily a girl's name.
Oikawa be like:
IWA CHAN!!!
CHIBI CHAN!!!!!
MAD DOG CHAAAAN
I said primarily as in that's the correct way to use it, besides Haikyuu is a different case
On page 18 En says "Onda? Why is she here?"
Also, she's referred to as "On-chan" by a classmate, which is a suffix most commonly used for females.