Underverse Eternal

Two years after Willow was destroyed and one year after Error's Death, the multiverse appeared to be at peace once again. That is, until it's attacked by Nightmare. Realizing this was a bigger threat, Blue goes to awaken the power of Eternity once again, which was sealed inside UnderBound Asriel. After his defeat, the multiverse is far from safe. A mysterious group known as the Colorstar Fairies show up. Their intentions are unknown to the others, but they have arrived because their AU was destroyed, leaving no trace behind. Not only that, a being of Darkness is going around and stealing the Code Cores of every AU in every multiverse. Asriel, Blue, and the others realize it is up to them to stop the darkness for once and for all, and save the multiverses.