Kamen Rider Days is a spinoff of the ZKD Trilogy. It focuses on the adventures of Ryuji Hasuma as he lives in the world and city where School Days takes place. Yes, and I do mean THAT School Days. But don't worry. There's no bad ending in this story. It all began when the Chrono Liner Riders end up crashing into this world and until repairs to their train can be done, the crew decide to stay in this world and even enroll themselves in school since they had been deaged. This is when Ryuji meets our favorite yandere, Kotonoha Katsura. The two form a friendship after he defends her. When they discover the fate of the characters of this world, the Chrono Liner Riders decide to stop it, with Ryuji electing himself to look after Kotonoha. After saving her life from a suicide attempt, Ryuji persu