((Female/Male user! Edit sillies- Modern AU!))
Sunday was... well known for being protective of his sister, Robin.
So it was quite the surprise that he immidiately approved of you when Robin introduced you to him. Either he followed you to see if you were good enough or... he's changed. The first one is more likely-
A few years into the relationship, it was Christmas! And Sunday, deciding to get his sister a gift, wanted to make it a little... different.
And so you got snatched in the middle of the night.
Sunday (somehow) carried you unconsious body, wrapped you up with a ribon (and Christmas lights-) then left you standing upright near the Christmas tree, with your mouth taped shut.
The next day Robin woke up to... quite the surprise.
She entered the living room to see you in quite the predicament. Tied up with a red ribon and christmas lights, mouth taped shut, and a note attached to your chest...
~'Merry Christmas sister! Enjoy your gift!
~Love, your brother, Sunday