Yumi's diary gets stolen by Hiroki, and to make matters worse, gets Lost at Sea by the Lyoko Warriors due to being sucked into a different hub. The crew have to find her before she succumbs to the digital sea.
This episode contains examples of:
- Annoying Younger Sibling: Hiroki proves to be this for Yumi when he steals her diary in order to please his crush Milly with a scoop for the Kadic newspaper.
- Big Brother Worship: Ulrich and Hiroki may not be related, but Hiroki treats Ulrich in this exact manner. He goes to Ulrich because he strongly admires him and wants to be like him; hence, why he goes to him for romance advice.
- Conveniently Interrupted Document: More like "Conveniently interrupted pages missing", but when Hiroki finds Yumi's diary in the leaf pile Odd set up, the pages are missing, and Yumi hates Hiroki even more. Ulrich gives a glare to Odd, who insists the diary was there when he set the scene up.
- Heroic BSoD: Ulrich undergoes a small one when Yumi is lost in the Digital Sea and they can't find her. He punches the inside of his ship and is very reluctant to leave without her (due to the Skid having low power and needing to be refueled). Jeremie somewhat calms him with the assurance he will still be searching for her, but Ulrich is still worried sick until she is found.
- Just in Time: The group saves Yumi just as William is about to permanently virtualize her in the Digital Sea. Just as he's about to blow up her ship, the Skid arrives in front of her, blocking the missile.
- Laser-Guided Karma: A rather harsh one. After Hiroki loses Yumi's diary, she disowns him, saying that until he finds it, he can consider himself an only child. When it seems that her diary is ruined, Yumi tells her brother that she'll never forgive him. Later, Yumi's Nav-Skid gets lost at the Digital Sea and she gets all alone, regretting the harsh treatment she gave to her brother earlier in the episode and not having made amends with him before what could be her death.
- Lost at Sea: The digital sea that is. The episode's general plot is to get her back by locating her, before she loses all power.
- Parting-Words Regret: Later averted, as Yumi does not actually die. But, while lost at the Digital Sea, Yumi regrets that the last thing she said to her brother was that she would never forgive him.
- Pet the Dog: Ulrich feels awful about Yumi getting mad with Hiroki for stealing and losing her diary, so he secretly tries to set things up so the two make up.
- Precocious Crush: Hiroki's crush on Milly is seen as this, given she is older than him.
- Secret Diary: Yumi has a secret diary that Hiroki stoles and then loses, much to her dismay.
- Shipper on Deck: Once again, Hiroki expresses how much he ships Yumi and Ulrich. When he tells Ulrich how his sister likes him, Ulrich shuts him down and insists he and Yumi are Just Friends. Hiroki remarks how "that's what she told [Ulrich]", getting Ulrich's attention. However, Hiroki changes the subject after this.
- What You Are in the Dark: Ulrich has the chance to read Yumi's private diary to see what she actually thinks of him, especially after seeing a photo of himself inside, but he refuses. Odd tells him how it's a golden opportunity, but he instantly refuses as "what's written [inside] is none of his business" and shows no temptation. He later secretly drops her diary off at her home to make it look like Hiroki gave it back, allowing the two siblings to make up and secretly watches with a smile.
