In case you hadn't figured it out yet, the vibrant girl happened to be none other than Delirium, the embodiment of Madness and Sanity, and the youngest of the Endless.
"Do you think you have imprisoned me? I will possess these chains and use them against you. And you will find me there, in front of your door, fighting the divine with the divine." I stated as my words disappeared into the vast emptiness of Tartarus, as darkness overwhelmed me.