It depends on the relationship and the circumstances.
Shojo Couples?
Fred Couples's birth name is Frederick Stephen Couples.
a written invitation or a phone call would be acceptable and proper
childless
eight, ate
Honey and cookie at least that is what i call my man and that is what he calls me
I would just call her by her name.
It would be best to call him by his name. If you don't know him, you can just call him sir.
Couple Square
eight, ate
No. VOCALOIDs are not couples. VOCALOIDs do not have to deal with anime or couples. It's only a singing program.
If they are married, they are referred to as a "married couple." If they are not married, usually the term "girlfriends" would apply.