Her stolen heart is the 59 episode of the series and the 7th episode of season Pure.
Lucia pinpoints the location of Seira's spirit in India. But before Seira's spirit merges with the orange pearl, Mikeru absorbs Seira within himself. Lucia must now collect the falling heart fragments of Seira, in order for her to be brought back to life.
At scool, Lucia saw Kaito having fun with Mikaru and also hearing the boys asking is Mikaru Kaito's girlfriend? Lucia came home and everyone at the Pearl Piari is pretending to act "normal": Hanon reading fashion trend, Rina laughing at a funny show talk, Nikora sweeping, Madane Taki reading the crystal ball, and Hippo brushing himself. Lucia ask what are they doing because Hanon is reading a pet magazine, Mikora is sweeping with a fishing rod, Rina not finding the news funny, Taki reading with a golden bowling ball, and Hippo brushing with a toilet-cleaning brush. Hippo accidently mention Kaito which Lucia ran into her room. In Mikaru's house, she is telling Rithio about what happen that was fun until she have a head ach causing her to be in bed. In the ocean the Black beauty sister have a sea snake and asked it to take them to the Indian Ocean. Mimi say that she can't wait to crush the pure soul that will be born soon and Sheshe say that she will enjoy watching her (meaning Seira) take her last breath. In Mikaru's bedroom, Mikaru asked Kaito to stay with her forever which Kaito said yes. Back at the Pearl Piari, Lucia is sad about what had happen with Kaito and she dreamed that Kaito called out her name but don't remember anything about her. Lucia woke up and went to Mikaru's house to see him. Lucia told Kaito to remember her and run away leaving Katio to say the she is a wierd girl. Lucia then walk alone until she heard Seira calling hear name. Seira told Lucia to hurry and that she is waiting for her in the Indian Ocean. Sara then appeared and told Lucia that it was time for Seira to be born and that Lucia is the only person who can teach Seira the wonderfulness of loving someone. Seira told Lucia to teach her and to open her doors of Destiny. Sara told Lucia to look at the Aurora and that when it breaks it will reveal the Dream corridor. The dream corridor brought Lucia into the sea. Sara's voice then explain that the Dream Corrider had brought Lucia into the Indian Ocean and that she would like Lucia to give back Seira her orange pearl. Lucia asked that the Ocean was where Sara was born and that the orange shell has a pretty orange color and that it was Sara's color. The shell throne opened and Sara told Lucia to put the orange pearl on it which she did. The pearl give an orange light and become bigger and bigger until Lucia saw Seira. Seira opened her eyes and was happy to see her. Lucia was happy but at the same time was alrert as she ask "Who's there!". The Black beauty sisters appeared and tells Lucia to give Seira to them. Seira was frighten so Lucia told them that she won't let them have her. Lucia transform and sung her song but it did not affect the sisters. Sheshe asked if Lucia had forgotten that any song won't affect them by only a single mermaid princess and they sang their song. Lucia was then de-transform and was reverted back into her mermaid form. Sheshe then told the sea snake to finish her. The seas snake wraped Lucia tightly that it was painful. Lucia was then droped on the ground and Mikeru appeared. He looked at Seira and said that he will take her purity with him. Lucia told to not harm Seira but Mikeru was not listening. Mikeru that asked Seira " You are temebling. Are you that scared of me? Well then, let me kindly embaces you!". Mikeru's wings grow bright and was reaching for Seira. Seira frightenly scream no as the wings absorbed her. All Lucia can do was watch because of her being attack. When Seira was completely abaorbed, all what was left was Seira's orange pearl. Lucia took the pearl was sad at what just had happen. Mikeru ask Lucia to join him because of her qualifications he was looking for but Lucia straight-foward refuse for Mikeru ruining Seira's new life and that she will never forgive him. Before Mikeru can take Lucia too Mikeru disappear leaving a feather behind. The sea snake dissapper and the Black beauty sisters left saying they will leave her punishment for the next time they meet. Sara's spirit appeared and Lucia apoligized to her for unable to protect Seira. Sara gave Lucia a compact that the pearl move into. Lucia took the compact from Sara and the orange pearl glow. Sara explain to Lucia that Seira is not gone for good but is just sleeping again inside of Mikeru. Lucia was relived that Seira were berelt alive. Sara asked Lucia to collect Seira's heart fragments and to bring her back before disappearing. The Idian ocean than become dark again and Lucia travel back to her place throught the Dream corridor thinking just like Seira's heart is sleeping within someone else, then Kaito's memories of her is sleeping within someone elso too. As sunrise came Lucia went to Mikaru's house and believes that she'll have to do anything she can to bring Kaito's memories back.