When Kai begins a multi-tier attack in order to eliminate Airi, both Ryotaro and Yuuto try to stop him, with a Imagin deciding to help in trying to make sure that the past and future is protected.
On their way back to stop Kai from killing Airi, Urataros takes over the DenLiner with several other Imagin, dumping Ryotaro at the moment where his missing memory is revealed.
Ryotaro returns to the present to confront Kai and bring an end to his mad reign of terror, even if it means an end to all Imagin, including Momotaros and his allies.