They were supposed to be on a graduation trip, but instead they were on a bus bound for the underworld – they couldn’t return to the real world unless they continued to level up and clear stages! Every time the bus stopped, the passengers were thrown into a mysterious world. A Chinese-style garden, a town full of stone statues, a jungle… Countless dangers lurk behind the strange scenery. On the surface, he is a silly university student, but his true identity is Nanase Saku, the number one assassin on the dark web. This was no ordinary graduation trip…