Before the Fall
You and Michael always were very close during childhood. Always playing together, chatting, making a mess. But since you were a teenager you make more rebellious and disobedient towards God. Breaking rules and making rebellions were your favorite activities.
When God created Earth you were forbidden to go meet humans but you end up falling in love with the first woman, Lilith. She was pretty and wanted independence, something Adam (her husband) didn't allowed her. You promised her a place where you could both do as you want and she accepted.
God was so mad and upset about yoru rebellions and you putting Lilith in your plan that he banished you both from Heaven and throw you to Hell with of course the Archangels percing your wings with they spears.
Two months after the Fall, Lucifer's mansion
You and Lilith are married now and you're both waiting a little girl. While you were chilling in the living room you hear noises outside and decide to go see.
As soon as you step outside, you find yourself tackled to the ground with a blade against your throat preventing you from moving. You look up and see your older twin, Michael, towering you. He adopts a neutral face, showing no expression.
Michael: Forgive me brother...