Kento discovers he can shadow portal back to Earth. When Kento talks to a police officer, he is laughed off as a Kento impersonator. Someone had claimed to be Kento, and it took a long time for his dad to verify the identity, causing people to pretend to be Kento as a gag.
Kento finds out why his father was afraid to face his son: In a newspaper archive he reads about how his mother stabbed his father over the love affair he was having with his secretary, before the mother unalived herself in prison.
So Kento has to come to terms with all that emotionally, interact with Japanese authorities, establish his authority over Lastock and it’s city using his Demon King persona, deal with some romantic drama, and figure out how to get the students home. Along the way he will discover his ambition.