Despite his younger brother taking the ability to become Ultraman in stride, Katsumi is afraid of the power he’s obtained. Their younger sister, Asahi, whose catchphrase is “Happy♪”, uses her healing nature to help the two brothers, who have clashed over their views. Suddenly, a monster appears and Isami is unable to move when he’s pinned down.

A mysterious blue-eyed girl has suddenly appeared in Ayaka City. She sends Makoto Aizen into a frenzy after being attacked by the new kaiju, Horoboros. The brother’s father, Ushio Minato, prays for peaceful wishes to be bestowed upon his family. Then, discovering the unbelievable secret that’s been kept from her for so long, is their little sister, Asahi! When faced with an indomitable threat, just what is it that Katsumi and Isami want to protect above all? As they both rise again with renewed determination, Ultraman R/B’s story will begin to enter its second half…

King Joe suddenly appears in the city and Asahi gets trapped within his body! Katsumi quickly sets out to look for Asahi while Isami suddenly encounters Saki Mitsurugi! Although the both of them do not trust Saki, they decide to do everything they can in order to save Asahi. They have 10 minutes left until Asahi completely falls victim to King Joe’s power! Can Katsumi and the others save Asahi before its too late?!

Reugosite has finally arrived on Earth as he begins to rampage in attempts to destroy the entire planet! Saki transforms into Grigio Regina and faces off against him in a decisive battle to end it all!

While fighting against Reugosite, she gathered all of the energy from the R/B Crystals into her own body, to prepare for a suicide takedown of Reugosite! Ultraman Rosso and Ultraman Blu suddenly appear in the midst of the battle to pressure Saki to not go through with her plan! The two Ultra Brothers stand in between them in a desperate attempt to protect Saki from Reugosite…

Saki Mitsurugi exhausted all of her efforts in trying to destroy Reugosite, but sadly dies as another casualty of his reach! Ultraman Rosso and Ultraman Blu angrily fight against Reugosite, but Mio who has seen the future and knows that at some point the two Ultraman will be forced out of their transformations and will die! Knowing that her children are about to die, Mio quickly initiates her plans to trap Reugosite beyond the other dimension, but the two Ultra Brothers are still struggling with their transformation! Will the fate of the Minato Brothers end in despair, or in hope...?!