"Reliving a Blank Day" (甦る空白の一日 Yomigaeru Kūhaku no Ichinichi) is the forty-fifth episode of Kamen Rider Den-O.
While getting the Milk Dipper ready for Christmas, Ryotaro receives a package holding a pocket watch, identical to the one Sakurai gave to Airi. Learning that the watch was sent to him by himself, with no recollection of the act, Ryotaro heads to the clock shop he and Airi went to last year for Sakurai's watch to get to the bottom of it. Learning that last year he ordered the watch for August, Ryotaro is even more confused and remembers Owner's words about his memory before going to find Yuto to take him to the day Airi lost her memory. But as Yuto refuses to help Ryotaro, hiding something from him, the clock shop owner inadvertently opens a contract with the Snowman Imagin. Once learning of the Snowman Imagin, Den-O Sword Form intercepts the Imagin and is unable to keep it from going back in time as he attempted not to destroy the Santa balloon in the vicinity. But in spite of Yuto's pleas not to, Ryotaro goes back in time to January 10, 2007, the day Sakurai disappeared and Airi lost her memory, to learn what truly happened. Once assuming Liner Form, Den-O destroys the Snowman Imagin and then Ryotaro heads to the lake where Sakurai disappeared. When he arrives, he sees Sakurai, as Zeronos Altair Form, fighting off a trio of Leo Soldiers before Kai opens a time pulse with the ZeroLiner covering Ryotaro and Yuto. In the midst of the explosion, Ryotaro sees Airi before she and Sakurai fade out of existence with the rest of the area. Only Ryotaro and Yuto remain, watching a jubilant Kai celebrating his victory on the desert wasteland.