Seraph of the End, Vol. 30 (manga)

Yu and Mikaela dive into the past in search of their oldest memories, and they pop out in a shocking time well before the birth of humanity…when dinosaurs roamed the earth! They continue on and run into an angel that looks suspiciously like Mikaela, who leads them to a mythical city with an enormous tower that extends into the heavens. What sort of mysteries will they encounter there?