Monty Paradise: The Wicked King and the Secret Memory

Heita Tsukigami fell asleep on the subway while going home. When he wakes up, he finds himself in a strange world called Montgomery Kingdom (in Monty Paradise), ruled by a wicked king, Pirithos.

Heita gets involved in a terrible situation, while encountering a mysterious girl, Emma.

In this world paradise, something strange happens with the memories, which determines one's fate.

(Not totally accurate)