Rinnosuke with eyelashes? DO NOT WANT.

That being said, Yuyuko doesn't even need to be undead to molest Youmu. That's kind scary.

It's her personality. Why would being undead be a prerequisite?

Because while being alive, she had enough common sense to seal the Saigyouji. When she started being dead, she became the Yuyuko we know, air-headed, and easily distracted, to the point that she forgot about her living self.

Having the sense to seal the Saigyou Ayakashi in no way indicates whether or not Yuyuko had the "playful molesting" part of her personality while she was alive.

Besides, she merely forgot about the Saiyougi's seal, plus she felt a bit lonely.

Neo_X said:
Besides, she merely forgot about the Saiyougi's seal, plus she felt a bit lonely.

Or simply doesn't know. We know she killed herself and we known her soul created the seal. Not sure it's ever been said for sure that the two were one and the same... a certain master of seals and borders might have created the seal so as to not waste her sacrifice.