Euphoria of the Soul

Cause let's face it-Flowey sure as heck seemed to be enjoying himself when he got all 6 of the human souls. ((I mean, he had that little sassy winky face when he said that line.))

And I would imagine a soulless ((SAD)) entity like Flowey would experience some degree of happiness with just ONE soul inside himself-let alone SIX ((and they're human souls, which makes them have even stronger of an impact)).