Already in the first episode it was clear how the plot of Yashahime: Princess half-demon was full of secrets and secrets that are slowly rising to the surface. In episode 21 of the anime, titled "The Secret of the Rainbow Pearls," Riku's true intentions and the origins of the seven pearls are revealed.
The episode's main focus, which is available for streaming on Crunchyroll, is the rainbow pearls apparently associated with Inuyasha's Shikon gem. owned by Lady Zero in the first flashback of the episode.
After searching for the big demon hound and learning of his death, Riku returns to his lover to let her know what happened. Shocked by the news, Lord Kirinmaru's sister breaks into a thunderous scream and uses the Shikon jewel to shed her demonic power and emotions and transform her Tears in the seven rainbow pearls. Although she transformed into a human in this flashback, Lady Zero is still alive about two hundred years later and is ready to eliminate the three protagonists.
This backstory also reveals some interesting details about Riku, as he is far from the ruse we are used to in the present. When he informed Lady Zero of the sad news, the boy did an innocent childlike air and he doesn't seem to really understand what's going on around him. Can we then see him referring to himself as a puppet during the episode that was being created at that moment?
This retrospective finally explains to the audience why Riku searches so intensely for the rainbow pearls. Zero's moment of pain seems to have had a strong influence on him and if he's looking for the pearls now, it's because they are nothing more than the tears of Kirnmaru's sister. In the previous episode of Yashahime, Setsuna's demonic side appeared.