Dantoudai no Hanayome - Sekai wo Horobosu Futsutsuka na Tatsuki desu ga.

A mythical beast emerges from a compartment that falls in front of Ryuunosuke Dazai. Inside is Rinne Irako, a striking winged serpent condemned to death as a disaster capable of destroying the world. Rinne is being transported to face her sentence when she encounters Ryuunosuke. Their meeting brings an ordinary young man into the path of a fearsome creature whose existence is considered a threat to the entire world.