ななみとこのみのおしえてA・B・C

You're a college student on summer vacation.
In your neighbourhood live two extremely friendly cute twin girls, Nanami and Konomi Nishimura.
One day their mother asks you to tutor the two of them.

"Nanami wants to study with onii-chan!"
"Onii-chan, will you teach Konomi?"

Of course, onii-chan immediately replies.