Sunny:
She asks you out by taking you out for a walk together and asking you during the walk.
Hitch:
He comes to your house with flowers and asks you.
Izzy:
She gets extremely excited and crafts a gift for you and asks you when you ask what the occasion was for the gift.
Zipp:
She shyly asks you when you are watching her fly around and show off.
Pipp:
She makes a song specially for you and sings it for you and asks you out through the song.