Kurosaki finally reunites with Ruri, and despite Kaito's suspicions, Kurosaki defends her. Watching the duel, the Doctor activates Parasite Fusioner, causing Ruri to turn on Kurosaki and challenge him to a duel. Kaito leaves to find the Doctor, and Kurosaki accepts Ruri's challenge. Kurosaki goes first and Xyz summons "Raidraptors - Rise Falcon." Kurosaki sets a card and ends his turn. Angered at an obvious trap and for Kurosaki looking down on her, Ruri draws and summons "Lyrical Luscinia - Cobalt Sparrow." Since Ruri controls a monster that is not "Lyrical Luscinia - Sapphire Sparow," its effect in her hand Special Summons it and another Lyrical Luscinia monster; Ruri chooses another Cobalt Sparrow. The effect of the Special Summoned Cobalt Sparrow adds the third copy of it to her hand, and summons it along with another copy of Sapphire Sparrow already in her hand.
Ruri overlays her five Level 1 monsters to Xyz summon "Lyrical Luscinia - Assembly Nightingale." The effect of Assembly Nightingale makes its ATK become equal to the number of overlay units it has times 100, and it can perform a number of direct attacks each turn equal to the number of overlay units it has. Nightengale attacks directly five times, swiftly bringing Kurosaki to 1500 Life Points. She ends her turn, declaring she does not belong to Kurosaki. Kurosaki activates "Rank-up Magic - Raid Force" and ranks up Rise Falcon into "Raidraptors - Blaze Falcon." Kurosaki activates Blaze Falcon's effect to destroy Nightingale, but Ruri uses Nightingale's effect to negate its destruction by detaching an Xyz unit. Blaze Falcon attacks directly and Ruri uses Nightingale's second effect to detach an Xyz unit and make the battle damage 0. Kurosaki ends his turn and Nightingale is down to 300 ATK.
Ruri's turn begins. She conducts three direct attacks with Nightingale, taking Kurosaki to 600 Life Points. In the depths of her mind Ruri begins to awaken, but the duel continues. Since a Lyrical Luscinia inflict damage, she activates the Quickplay spell "Lyrical Luscinia - Bird Song" to summon a level 1 monster from her hand. She summons "Parasite Fusioner," stunning Kurosaki. As it was Special Summoned, Parasite Fusioner lets Ruri perform a Fusion Summon instantly. She fuses Nightingale and Fusioner to summon "Lyrical Luscinia - Independent Nightingale" with 1000 ATK. The effect of Parasite Fusioner equips itself to Nightingale, and the effect of Nightingale activates. Its level increases by 1 for each Xyz unit Assembly Nightingale had, and it gains 500 ATK times its level. Now level 4, Independent Nightingale climbs to 3000 ATK.
Nightingale attacks Blaze Falcon, and Kurosaki activates his Trap "Raidraptor - Evasive" to return an Xyz unit to his hand and negate the attack. Ruri activates Nightingale's effect to deal 500 damage times its level, but Kurosaki finds the Action card "Acceleration" to negate the effect damage. Ruri activates "Lyrical Luscinia - Bird Strike" to negate Blaze Falcon's effect, and ends her turn. Kurosaki draws, and is surprised by what he sees. He reminds Ruri of when she duels Sayaka and lost. Sayaka tried to give her "Little Fairy" card to Ruri, but Kurosaki slapped it away, telling her not to accept cards from others. Kurosaki admits he was angry over her loss, and couldn't understand Sayaka then. However, after meeting Yuya and the Lancers, he does.
Kurosaki summons "Little Fairy," given to him by Kaito. He uses its effect twice to increase its level to 5. He then activates "Cross Xyz." Since Little Fairy's level is the same as Blaze Falcon's Rank, Kurosaki can treat Blaze Falcon as having a level and use the two of them to Xyz Summon. He overlays them to summon "Raidraptor - Étranger Falcon." Kurosaki uses Étranger Falcon's effect, detaching an Xyz unit to destroy Independent Nightingale and deal damage equal to its ATK. Ruri begins to use the effect of Parsite Fusioner to negate Nightingale's destruction, but her true self fights back and stops the move. Nightingale is destroyed and Ruri is down to 1000 Life Points. In control of her body, Ruri calls for Kurosaki to attack her. He does so, winning the duel. Ruri is freed from the Doctor's control, but he runs off laughing he knows ways to improve his methods.
Meanwhile in the battle arena, Sawatari falls down a cliff to escape his pursuer. He climbs up to find Crow. The Academia duelists Emma and Jacob find them, and they begin a tag team duel. Suddenly, their duel disks announce an intrusion penalty has been inflicted - someone else has entered the duel, but there is no one there. Crow calls on the new duelist to show themselves. Watching in the bushes, Sanders' Battle Beast prepares to strike.
This episode contains the following tropes:
- Big Brother Instinct: Inverted. It is Ruri who bails out Kurosaki before her corrupted self can finish him off.Corrupted Ruri: I can deal with that By sending Parasite Fusioner to the Graveyard, I can negate the destruction Ah My hand!Original Ruri: I won't let you!
- Flash Step: Kurosaki is seen dodging an attack from one of Ruri's monsters simply by sliding left with a trace image.
- Fighting from the Inside: In the last turn, Ruri was able to fight against the Doctor's brainjacking and let her brother win the Duel. Time will only tell if she is completely freed.
- Glory Hound: Oh Sawatari, you never learn, do you?
- Honor Before Reason: Kurosaki was used to be a Jerkass who values honor to the point where he slaps "Little Fairy" from Ruri's hand.
- Ironic Echo: Ruri repeatedly attacking Shun with Assembly Nightingale and counting off the attacks brings to mind Shun's earlier smackdown of Dennis using Satellite Cannon Falcon.
- Meaningful Name: This episode refers to Ruri, who is forced to face Kurosaki in a Duel by the Doctor while fighting the influence of the Parasite Fusioner.
- Mythology Gag: The Japanese title of this episode is "Yami ni Ochita Kotori".
- Plot Armor:
Sawatari: Just who is he? Whos this guy chasing after me?
- Ruri gives one to Kurosaki by holding off the Doctor's Parasite Fusioner at the last second and throwing herself out of the ring. Granted, since Kurosaki would be carded if Ruri wins the Duel.
- Turns out that the Battle Beast is chasing Sawatari like a wild animal the whole time.
- Resist the Beast: Not even the Doctor can stop Ruri from saving her brother.
- Suicide by Cop: This is how Ruri lost the Duel to Kurosaki, although the Doctor is not surprised about it.Kurosaki: Is that you, Ruri!?Ruri: Brother, finish me off!
- Wham Episode:
- The Parasite Fusioner's brainjacking effect is not absolute: If a bracelet girl is strong-willed, she can fight back.
- Although Ruri succeeds in helping Kurosaki beat her corrupted self, the Doctor reveals that he has other plans.