Same person, Just not in the Same Body. (Reincarnated as Dream & Nightmare)

What if..Someone got Reincarnated as Both Dream AND Nightmare? But..their Personalities Split into Two?

Dream as Their Positive Feelings and Emotion.
Nightmare as Their Negative Feelings and Emotion.

But..Dream has some..Fake Feelings and Emotion. as of which is 'Happiness' 'Love' and 'Excitement' But does Genuinely Care about others.

Nightmare having VERY Negative Feelings and Emotions. Such as Self-hate, Depression and Anger.

How will Such two Different Personalities cope with Each other Despite the fact Of Being Complete Opposites?

Well...let's find out, Shall we..?